portraits.2da, heads.2da and appearance.2da are linked files, you will likely need to check those files as well, because they each refrence one another. This might be the cause of your portrait reversion problem.
appearance.2da refrences heads.2da, and heads.2da refrences portraits.2da. So if you are making a new NPC, you will need to edit entries in those 3 files. ;)
This tutorial (
http://64.20.36.211/showthread.php?t=131944) might be of some help in this endeavour.
I hope this helps! :D
@ Welcome to the forums! :waive1: