I’m not quite sure how to insert portraits myself, but you can swap around portraits by simply changing their file names. You’d essentially need to find out how fe11 encrypts, and decrypts it’s files, or rather what format they are in. I recall HeartHero figuring out how it works and making an (unreleased) portrait editor for fe12.
Your best call would probably be to ask him.
This is the thread i’m referring to, although privately contacting him would probably be for the better