[LG V30 Guides, News, & Discussion] Ascii3:
Thanks [MENTION=5906767]tech_infinity[/MENTION] and [MENTION=3250376]ChazzMatt[/MENTION] for the various warnings regarding Android Pie and Android Oreo stock firmware compatibility. However, there are some important questions that still remain:

What permanent changes are made by flashing Android Pie KDZ files?

Are the changes made by flashing Android Pie KDZ files truly permanent or simply more difficult to revert than simply flashing a KDZ file? (For example, blowing a fuse could be considered truly permanent, but writing a particular value to NVRAM may just be considered more difficult to revert.) Perhaps flashing an LGUP DUMP of original LG Oreo using LGUP's PARTITION DL may result in a correct downgrade.

The troubles with different LG V30 US998 firmware's blobs reminds me of something which seems similar with the LG G5 RS988. For that device while running the latest non-very defective firmware, RS98821d, many custom ROMS of Android Pie or Android 10 would misbehave if an Android Oreo based custom ROM is not used before Android Pie or Android 10. The workaround if already running Android Pie or Android 10 based custom ROMS was to backup the current /system and /data partitions, then (optionally wipe and then) flash an Android Oreo-based custom ROM, boot the Android Oreo-based custom ROM, then restore the previous Android Pie or Android 10 backup. I wrote more about this issue at: https://xdaforums.com/showpost.php?p=82947529&postcount=49 .

Other than the troubles using Android Pie or Android 10 custom ROMs that may result, does flashing to earlier firmware via KDZ file actually work well for the LG V30 US998?

My experience with another LG device, the LG G5 RS988.USA, is that flashing older firmware via LGUP 1.14.03 does not work well. On that device, I was using the latest RS988.USA firmware available via Over-The-Air update and was running stock Android Nougat. The bootloader had already been unlocked and TWRP recovery was installed. Using TWRP, I flashed a complete/full firmware ZIP file of Android Marshmallow that was presented in one of the XDA firmware threads. I then locked the bootloader via fastboot command, then rebooted to the LG LAF flasher (download mode) and used the original LGUP 1.14.03 with the UPPERCUT crack to REFURBISH flash the Android Marshmallow KDZ file that corresponded to the firmware version of the complete/full firmware ZIP file that I flashed using TWRP. After the flash, the system would boot, but the behavior was odd and some things would not work or be properly available. I flashed the Android Marshmallow KDZ firmware file via LGUP 1.14.03 again, but it did not seem to fix anything. To get the device properly functioning again, I had to flash back to fully-updated Android Noguat again via Over-The-Air updates (The RS988 unfortunately did not have an Android Nougat KDZ firmware file that corresponded to the latest firmware provided for RS988.USA). Interestingly, the system downloaded what appeared to be all Over-The-Air updates individually and flashed them, rather than just using the Over-The-Air updates that would normally apply when trying to update from the Android Marshmallow firmware. No update changed the general Anti-Rollback counter. I provided more details of the happening at: https://xdaforums.com/showpost.php?p=82338329&postcount=3 .