[Galaxy Note 3 Q&A, Help & Troubleshooting] perosredo:
Somewhere over the years I apparently lost the carrier directory in /efs, as well as the CSC data - is there any way of getting this back? I'm hoping it's at least possible by flashing back to stock but only as a last resort - I've tried a bunch of different things without success so far.

The phone started as a Rogers N900W8 and was immediately unlocked and rooted. Sometime soon thereafter a Bell 4.3 firmware was flashed (via Heimdall). I then switched from Rogers to Wind (now Freedom) - I believe this is where the hidden menu disappeared if I remember correctly - and the phone functioned just fine through all of this.

I then moved from that Bell BMC 4.3 to the Wind GLW PG1 5.0 firmware (grabbed from sammobile and flashed via Odin) thinking that the presence of the Wind SIM would trigger the firmware to switch from BMC to GLW but it doesn't seem to have worked out like that. I'm now running the LineageOS nightlies and the phone works just fine except for a lack of LTE which is what I'd like to sort out with the secret codes. Also, since switching to Wind I believe my mobile network has always been displayed as HOME.

Samsung Phone Info doesn't list any CSCs except BMC under original. In the firmware tab, it's not listing PDA or CSC version. There is no carrier directory in /efs nor are there any CSC files in the file system. Entering almost any secret code fails "Connection problem or invalid MMI code" - *#06# will display IMEI but all others I've tried don't work.

UPDATE #1:

Have been able to get the Canadian CSCs onto the device and recognizable as being present by Phone Info.

Ripped out cache.img.ext4 from the PG1 firmware and used Cache Ripper (found on XDA somewhere) via Wine on linux to create a TWRP flashable zip. Had to mount system in TWRP before flashing.

Changing CSC with Phone Info apparently does a Factory Reset and not quite ready to do that yet as more research seems to point to reverting to stock for the hidden menu.

UPDATE #2:

Flashed stock PG1 via Odin. Went into a bootloop after building Dalvik on first boot and had to reboot into the stock recovery and wipe data and system, then it booted fine. The back button stopped working (LOL Samsung) and I had to flash a random 5.0 custom kernel (idlekernel) to get it back. Flashed TWRP and SuperSU.

There is now an empty carrier directory in root but there still isn't one in /efs. Lots of information on XDA pointing to this being a prerequisite for the secret codes - turns out it's all bunk.

Secret codes work. Had some difficulties with Phone Info not letting me into the root menus to change CSC - was spitting out output from some failed scripts - and when I was just about to give up it started working. Changed CSC to GLW which prompted another factory reset, and now it shows GLW / BMC as the active CSCs. APNs were Bell's originally, which is not what I wanted, but after following the *#272*IMEI directions from this thread and another factory reset they are now Wind's. No LTE yet. Would like to get rid of the BMC CSCs altogether since this was never a Bell device.

Some more stuff changed in Phone Info: Product Name is now hltevl, Firmware's CSC Code is now BMC and CSC Country is Canada/CA. PDA and CSC version has also been populated. CSC Changer still defaults to having BMC selected and I'm still getting the Bell bloatware.

UPDATE #3:

Active CSC reverted to BMC after a couple reboots...they're all BMC now.