Not Sure How to Do This? (Changing Portraits)

[BrokenGrace]

So I've been playing around with FE11 for a little while now and have had my fun playing with Growth Rates and Base Stats as well as playing around with item stats. (Still haven't cracked the limitations on certain items, but I'll get there.)

Anyway, so what I'm currently trying to do right now is change portraits in the game. Specifically remove portraits from the game and replace them with custom ones I made. (There were just a couple of changes I made with some of them and I made one to replace post-prologue Marth, nothing wrong with his face really, it's just a really awkward angle.)

Naturally as one might expect with my limited knowledge on hacking and what knowledge I do have being provided by Nightmare. I'm not too sure how to approach this. I keep looking through the decompiled data but I can't seem to even find the portraits and I'm not sure how I'd go about changing them, since Nightmare only gives me the ability to swap between pre-existing portraits and not replace portraits with something else.

If anyone is has knowledge on the subject and has the patience to explain to me what to do I'd greatly appreciate it.