yeah i kinda managed to find out about that, but im having problems with it and also file size
initial d psp tools warn you if you try to replace a file bigger or smaller than the original one, it has a option to "fix" that but i just get a blackscreen when i enter the menu where i modified a texture
basically it have to be exact same size.
if i use Photoshop, open the original gim and paste my edited png it will be the same file size but with no transparent background, works ingame, tried the same method i was using for a transparent png with indexed color
if i use gimconv my final .gim gets smaller or bigger but with transparent background, doesnt work ingame
so idk what should i do now, i found 0 documentation about this .gim plugin, and for gimconv there are some notes from the guy who made Initial D PSP Tools, but as i explained, doesnt work ingame...