Agreed, it's best to use rePatch instead of the game's actual installation directory. That way you don't have to reinstall the game if something goes wrong, and it's less data to transfer too. Using the
custom eboot, you can make a brand new cpk (named mod.cpk) containing only the modified files. Makes it easier to diagnose why it might not be working, too. I've never used cripakgui's patch feature so idk if maybe the program put battle_pack.bin in the wrong directory of the cpk instead of replacing the original file.
Then again, P4G has a bunch of redundant duplicate files so I'm not always sure which ones are actually used or not. There's battle_pack.bin and battle_pack2.bin, and then also btlpanel.bin and btlpnlop.bin in the panel folder. To be on the safe side I'd just replace all the Yu icons in each of them.
Either way I recommend installing the AutoPlugin VPK from
here with Vitashell and using the app it installs to get repatch so that you don't have to worry about configuring it. From there, you can put your mod.cpk in ux0:rePatch/PCSE00120/data/mod.cpk and EBOOT goes in ux0:rePatch/PCSE00120/EBOOT.BIN.
As for making a new cpk from scratch instead of using the patch function, there's a couple ways to go about that. Easiest way in my opinion is using the
Mod Compendium. Clicking the New button will generate a folder for your mod, and from there you can put your new file in like this:
ModCompendium\Mods\Persona4Golden\YourModName\Data\battle\panel\btlpanel.bin
then it's just a matter of setting the Output Directory of your new cpk in the settings and clicking Build and transferring it over to your Vita.
Alternatively there's
cripackedfilemaker which should be able to make a new cpk from a folder (matching the structure of the extracted cpk) like so:
C:\Users\Username\Desktop\Mod\battle\panel\btlpanel.bin
(the "Mod" folder in this example would be the one you choose to build the cpk from)