How do you do this in Project M?
I've yet to try this but I believe if you have a copy of project M in a normal folder then you may freely tinker with the specific common5.pac data in the folder using brawlbox and then replace the old data that's in the sd card using winimage. Will update if successful.
Edit1: So for project M common5.pac is empty, the portraits are probably in another common pac
Edit2: So none of the common.pacs had portrait data in them but I managed to find some "MenSelchrFace" data in projectm/pf/menu/common/char_bust_tex
There aren't enough files to cover every character portrait so either thats not what these are or theyre only the new projectm-exclusive portraits.
Edit3: JK, these are the portraits, you just have to open a specific "MenSelchrFace" to reveal the additional palettes for each character.
Edit4: I'm replacing the old portrait image as instructed above but the program isn't letting me change "Has Palette" to "true". The dimensions for the image are right and the preview looks good.
Edit5: Alright, to switch the "Has Palette" to "true" you must select image format CI8(or similar formats). This gives the portrait a palette.
Edit6: SUCCESS! Sort of. I replaced the image it shows of your character at end-game screen where it shows your kills/deaths/etc.
Edit7: Found the buggers. C:\Users\YourName\Desktop\Project M\projectm\pf\menu2
Your copy of pm thats NOT on your SD card is where you can find and tinker with these, then its a simple "insert folder" (menu2) using winimage to replace the one on your sd card.