[G2 and Desire Z Q&A, Help & Troubleshooting] XVI Ames:
Yes, I did it through the bootloader ;)

Since it was still stuck on updating radio, I removed the battery and tried again, without success (same errors, and even an error on recovery update).

But I have found the following thread GUIDE: Downgrading for those with the PC10IMG.zip not found issue, and tried this method... it seems to have worked:

(bootloader) [RUU]UZ,system,94
(bootloader) [RUU]UZ,system,94
(bootloader) [RUU]UZ,system,95
(bootloader) [RUU]UZ,system,96
(bootloader) [RUU]UZ,system,96
(bootloader) [RUU]UZ,system,97
(bootloader) [RUU]UZ,system,98
(bootloader) [RUU]UZ,system,98
(bootloader) [RUU]UZ,system,99
(bootloader) [RUU]UZ,system,100
(bootloader) [RUU]WP,system,91
(bootloader) [RUU]WP,system,94
(bootloader) [RUU]WP,system,97
(bootloader) [RUU]WP,system,100
(bootloader) start image[userdata] unzipping & flushing...
(bootloader) [RUU]UZ,userdata,0
(bootloader) [RUU]UZ,userdata,0
(bootloader) [RUU]UZ,userdata,1
(bootloader) [RUU]UZ,userdata,1
(bootloader) [RUU]UZ,userdata,2
(bootloader) [RUU]UZ,userdata,3
(bootloader) [RUU]UZ,userdata,4
(bootloader) [RUU]UZ,userdata,4
(bootloader) [RUU]UZ,userdata,5
(bootloader) [RUU]UZ,userdata,6
(bootloader) [RUU]UZ,userdata,6
(bootloader) [RUU]UZ,userdata,7
(bootloader) [RUU]UZ,userdata,8
(bootloader) [RUU]UZ,userdata,8
(bootloader) [RUU]UZ,userdata,9
(bootloader) [RUU]UZ,userdata,10
(bootloader) [RUU]UZ,userdata,11
(bootloader) [RUU]WP,userdata,0
(bootloader) [RUU]WP,userdata,1
(bootloader) [RUU]WP,userdata,2
(bootloader) [RUU]WP,userdata,4
(bootloader) [RUU]WP,userdata,5
(bootloader) [RUU]WP,userdata,6
(bootloader) [RUU]WP,userdata,8
(bootloader) [RUU]WP,userdata,9
(bootloader) [RUU]WP,userdata,11
(bootloader) [RUU]UZ,userdata,11
(bootloader) [RUU]UZ,userdata,11
(bootloader) [RUU]UZ,userdata,12
(bootloader) [RUU]UZ,userdata,13
(bootloader) [RUU]UZ,userdata,14
(bootloader) [RUU]UZ,userdata,14
(bootloader) [RUU]UZ,userdata,15
(bootloader) [RUU]UZ,userdata,16
(bootloader) [RUU]UZ,userdata,17
(bootloader) [RUU]UZ,userdata,17
(bootloader) [RUU]UZ,userdata,18
(bootloader) [RUU]UZ,userdata,19
(bootloader) [RUU]UZ,userdata,20
(bootloader) [RUU]UZ,userdata,20
(bootloader) [RUU]UZ,userdata,21
(bootloader) [RUU]UZ,userdata,22
(bootloader) [RUU]UZ,userdata,23
(bootloader) [RUU]WP,userdata,11
(bootloader) [RUU]WP,userdata,15
(bootloader) [RUU]WP,userdata,17
(bootloader) [RUU]WP,userdata,18
(bootloader) [RUU]WP,userdata,20
(bootloader) [RUU]WP,userdata,21
(bootloader) [RUU]WP,userdata,23
(bootloader) [RUU]UZ,userdata,23
(bootloader) [RUU]UZ,userdata,23
(bootloader) [RUU]UZ,userdata,24
(bootloader) [RUU]UZ,userdata,25
(bootloader) [RUU]UZ,userdata,26
(bootloader) [RUU]UZ,userdata,26
(bootloader) [RUU]UZ,userdata,27
(bootloader) [RUU]UZ,userdata,28
(bootloader) [RUU]UZ,userdata,29
(bootloader) [RUU]UZ,userdata,29
(bootloader) [RUU]UZ,userdata,30
(bootloader) [RUU]UZ,userdata,31
(bootloader) [RUU]UZ,userdata,32
(bootloader) [RUU]UZ,userdata,32
(bootloader) [RUU]UZ,userdata,33
(bootloader) [RUU]UZ,userdata,34
(bootloader) [RUU]UZ,userdata,35
(bootloader) [RUU]WP,userdata,23
(bootloader) [RUU]WP,userdata,24
(bootloader) [RUU]WP,userdata,26
(bootloader) [RUU]WP,userdata,27
(bootloader) [RUU]WP,userdata,29
(bootloader) [RUU]WP,userdata,30
(bootloader) [RUU]WP,userdata,32
(bootloader) [RUU]WP,userdata,33
(bootloader) [RUU]WP,userdata,35
(bootloader) [RUU]UZ,userdata,35
(bootloader) [RUU]UZ,userdata,35
(bootloader) [RUU]UZ,userdata,36
(bootloader) [RUU]UZ,userdata,36
(bootloader) [RUU]UZ,userdata,37
(bootloader) [RUU]UZ,userdata,38
(bootloader) [RUU]UZ,userdata,39
(bootloader) [RUU]UZ,userdata,39
(bootloader) [RUU]UZ,userdata,40
(bootloader) [RUU]UZ,userdata,41
(bootloader) [RUU]UZ,userdata,41
(bootloader) [RUU]UZ,userdata,42
(bootloader) [RUU]UZ,userdata,43
(bootloader) [RUU]UZ,userdata,43
(bootloader) [RUU]UZ,userdata,44
(bootloader) [RUU]UZ,userdata,45
(bootloader) [RUU]UZ,userdata,46
(bootloader) [RUU]WP,userdata,35
(bootloader) [RUU]WP,userdata,36
(bootloader) [RUU]WP,userdata,37
(bootloader) [RUU]WP,userdata,39
(bootloader) [RUU]WP,userdata,40
(bootloader) [RUU]WP,userdata,41
(bootloader) [RUU]WP,userdata,43
(bootloader) [RUU]WP,userdata,44
(bootloader) [RUU]WP,userdata,46
(bootloader) [RUU]UZ,userdata,46
(bootloader) [RUU]UZ,userdata,46
(bootloader) [RUU]UZ,userdata,47
(bootloader) [RUU]UZ,userdata,48
(bootloader) [RUU]UZ,userdata,49
(bootloader) [RUU]UZ,userdata,49
(bootloader) [RUU]UZ,userdata,50
(bootloader) [RUU]UZ,userdata,51
(bootloader) [RUU]UZ,userdata,52
(bootloader) [RUU]UZ,userdata,52
(bootloader) [RUU]UZ,userdata,53
(bootloader) [RUU]UZ,userdata,54
(bootloader) [RUU]UZ,userdata,55
(bootloader) [RUU]UZ,userdata,55
(bootloader) [RUU]UZ,userdata,56
(bootloader) [RUU]UZ,userdata,57
(bootloader) [RUU]UZ,userdata,58
(bootloader) [RUU]WP,userdata,46
(bootloader) [RUU]WP,userdata,47
(bootloader) [RUU]WP,userdata,49
(bootloader) [RUU]WP,userdata,50
(bootloader) [RUU]WP,userdata,52
(bootloader) [RUU]WP,userdata,53
(bootloader) [RUU]WP,userdata,55
(bootloader) [RUU]WP,userdata,56
(bootloader) [RUU]WP,userdata,58
(bootloader) [RUU]UZ,userdata,58
(bootloader) [RUU]UZ,userdata,58
(bootloader) [RUU]UZ,userdata,59
(bootloader) [RUU]UZ,userdata,60
(bootloader) [RUU]UZ,userdata,61
(bootloader) [RUU]UZ,userdata,61
(bootloader) [RUU]UZ,userdata,62
(bootloader) [RUU]UZ,userdata,63
(bootloader) [RUU]UZ,userdata,64
(bootloader) [RUU]UZ,userdata,64
(bootloader) [RUU]UZ,userdata,65
(bootloader) [RUU]UZ,userdata,66
(bootloader) [RUU]UZ,userdata,67
(bootloader) [RUU]UZ,userdata,67
(bootloader) [RUU]UZ,userdata,68
(bootloader) [RUU]UZ,userdata,69
(bootloader) [RUU]UZ,userdata,70
(bootloader) [RUU]WP,userdata,58
(bootloader) [RUU]WP,userdata,59
(bootloader) [RUU]WP,userdata,61
(bootloader) [RUU]WP,userdata,62
(bootloader) [RUU]WP,userdata,64
(bootloader) [RUU]WP,userdata,65
(bootloader) [RUU]WP,userdata,67
(bootloader) [RUU]WP,userdata,68
(bootloader) [RUU]WP,userdata,70
(bootloader) [RUU]UZ,userdata,70
(bootloader) [RUU]UZ,userdata,70
(bootloader) [RUU]UZ,userdata,71
(bootloader) [RUU]UZ,userdata,72
(bootloader) [RUU]UZ,userdata,73
(bootloader) [RUU]UZ,userdata,73
(bootloader) [RUU]UZ,userdata,74
(bootloader) [RUU]UZ,userdata,75
(bootloader) [RUU]UZ,userdata,76
(bootloader) [RUU]UZ,userdata,76
(bootloader) [RUU]UZ,userdata,77
(bootloader) [RUU]UZ,userdata,78
(bootloader) [RUU]UZ,userdata,79
(bootloader) [RUU]UZ,userdata,79
(bootloader) [RUU]UZ,userdata,80
(bootloader) [RUU]UZ,userdata,81
(bootloader) [RUU]UZ,userdata,82
(bootloader) [RUU]WP,userdata,70
(bootloader) [RUU]WP,userdata,71
(bootloader) [RUU]WP,userdata,73
(bootloader) [RUU]WP,userdata,74
(bootloader) [RUU]WP,userdata,76
(bootloader) [RUU]WP,userdata,77
(bootloader) [RUU]WP,userdata,79
(bootloader) [RUU]WP,userdata,80
(bootloader) [RUU]WP,userdata,82
(bootloader) [RUU]UZ,userdata,82
(bootloader) [RUU]UZ,userdata,82
(bootloader) [RUU]UZ,userdata,83
(bootloader) [RUU]UZ,userdata,83
(bootloader) [RUU]UZ,userdata,84
(bootloader) [RUU]UZ,userdata,85
(bootloader) [RUU]UZ,userdata,86
(bootloader) [RUU]UZ,userdata,86
(bootloader) [RUU]UZ,userdata,87
(bootloader) [RUU]UZ,userdata,88
(bootloader) [RUU]UZ,userdata,88
(bootloader) [RUU]UZ,userdata,89
(bootloader) [RUU]UZ,userdata,90
(bootloader) [RUU]UZ,userdata,90
(bootloader) [RUU]UZ,userdata,91
(bootloader) [RUU]UZ,userdata,92
(bootloader) [RUU]UZ,userdata,93
(bootloader) [RUU]WP,userdata,82
(bootloader) [RUU]WP,userdata,83
(bootloader) [RUU]WP,userdata,84
(bootloader) [RUU]WP,userdata,86
(bootloader) [RUU]WP,userdata,87
(bootloader) [RUU]WP,userdata,88
(bootloader) [RUU]WP,userdata,90
(bootloader) [RUU]WP,userdata,91
(bootloader) [RUU]WP,userdata,93
(bootloader) [RUU]UZ,userdata,93
(bootloader) [RUU]UZ,userdata,93
(bootloader) [RUU]UZ,userdata,93
(bootloader) [RUU]UZ,userdata,94
(bootloader) [RUU]UZ,userdata,94
(bootloader) [RUU]UZ,userdata,95
(bootloader) [RUU]UZ,userdata,95
(bootloader) [RUU]UZ,userdata,95
(bootloader) [RUU]UZ,userdata,96
(bootloader) [RUU]UZ,userdata,96
(bootloader) [RUU]UZ,userdata,97
(bootloader) [RUU]UZ,userdata,97
(bootloader) [RUU]UZ,userdata,97
(bootloader) [RUU]UZ,userdata,98
(bootloader) [RUU]UZ,userdata,98
(bootloader) [RUU]UZ,userdata,99
(bootloader) [RUU]UZ,userdata,99
(bootloader) [RUU]UZ,userdata,100
(bootloader) [RUU]WP,userdata,93
(bootloader) [RUU]WP,userdata,94
(bootloader) [RUU]WP,userdata,96
(bootloader) [RUU]WP,userdata,97
(bootloader) [RUU]WP,userdata,99
(bootloader) [RUU]WP,userdata,100
(bootloader) start image[sp1] unzipping & flushing...
(bootloader) [RUU]UZ,sp1,0
(bootloader) [RUU]UZ,sp1,100
(bootloader) [RUU]WP,sp1,0
(bootloader) [RUU]WP,sp1,100
(bootloader) start image[sp2] unzipping & flushing...
(bootloader) [RUU]UZ,sp2,0
(bootloader) [RUU]UZ,sp2,100
(bootloader) [RUU]WP,sp2,0
(bootloader) [RUU]WP,sp2,100
(bootloader) start image[dzdata] unzipping & flushing...
(bootloader) [RUU]UZ,dzdata,0
(bootloader) [RUU]UZ,dzdata,100
(bootloader) [RUU]WP,dzdata,0
(bootloader) [RUU]WP,dzdata,100
(bootloader) start image[tp] unzipping & flushing...
(bootloader) [RUU]UZ,tp,0
(bootloader) [RUU]UZ,tp,100
(bootloader) [RUU]WP,tp,0
(bootloader) start image[tp] unzipping & flushing...
(bootloader) [RUU]UZ,tp,0
(bootloader) [RUU]UZ,tp,100
(bootloader) start image[radio] unzipping & flushing...
(bootloader) [RUU]UZ,radio,0
(bootloader) [RUU]UZ,radio,8
(bootloader) [RUU]UZ,radio,13
(bootloader) [RUU]UZ,radio,20
(bootloader) [RUU]UZ,radio,25
(bootloader) [RUU]UZ,radio,33
(bootloader) [RUU]UZ,radio,41
(bootloader) [RUU]UZ,radio,49
(bootloader) [RUU]UZ,radio,57
(bootloader) [RUU]UZ,radio,62
(bootloader) [RUU]UZ,radio,70
(bootloader) [RUU]UZ,radio,79
(bootloader) [RUU]UZ,radio,86
(bootloader) [RUU]UZ,radio,94
(bootloader) [RUU]UZ,radio,99
(bootloader) [RUU]UZ,radio,100
(bootloader) [RUU]WP,radio,0
(bootloader) [RUU]WP,radio,6
(bootloader) [RUU]WP,radio,14
(bootloader) [RUU]WP,radio,19
(bootloader) [RUU]WP,radio,27
(bootloader) [RUU]WP,radio,36
(bootloader) [RUU]WP,radio,44
(bootloader) [RUU]WP,radio,100
(bootloader) start image[rcdata] unzipping & flushing...
(bootloader) [RUU]UZ,rcdata,0
(bootloader) [RUU]WP,rcdata,0
(bootloader) [RUU]WP,rcdata,100
OKAY [185.175s]
finished. total time: 233.504s

But the phone still did not boot...

I got back to the hboot, and tried update again, and at this point, it seems to work too, everything was ok (or bypassed for the second TP), I hitted power button to reboot, HTC logo came, then the annoying HTC sound with the "quietly brilliant" logo and... android starts ! \o/

I think I'm not done yet, but it is on a good way!