Odd IMEI situation (Nexus 6 AT&T)

So I've been playing with my Nexus 6 (I am the original owner) for a while, and recently PCS'd to South Korea for 3-5 years.

AT&T suspended my wireless service under the Soldiers/Sailors Relief Act, which basically suspends my service for $.01/mo.

Now, AT&T also allows you to unlock your device so that you can use a local SIM in the country you are stationed, however their online support unlock request form does NOT recognize my IMEI???

Is it even remotely possible that flashing other radios/bootloaders/roms can potentially modify the IMEI? If so, how can I go about getting the original IMEI restored? I believe I flashed the Google-Fi rom/radio/bootloader most recently. Should I flash back a stock LMY47E or something like that with radios etc.?

I don't normally ask questions like this, but it has stumped me for the last 4 days and I've done lots of searching with no results. My google-fu sucks apparently.

Thanks in advance.