Persona Q2 is the sequel to Persona Q, a spinoff title in the Persona franchise, developed as a joint collaboration between Atlus's Persona team and the Etrian Odyssey team. It features the nearly complete cast of playable characters from Persona 3, Persona 4 and Persona 5. In this game, each party member is available immediately and all have the Wild Card ability, which means they can use any Persona. However, you no longer have the ability to switch Personas mid-battle.
Similar to Persona 5, modded files can be placed in a new CPK that overrides the original data.cpk so that you don't have to repack the entire CPK to make changes. Check out DeathChaos's Mod.cpk Patch. Use the Mod Compendium to build a new CPK containing your modified files (use compression). Note: this patch comes with a modification that allows you to permanently rename the protagonists and uses their latest canon names by default. Read the instructions on the github page for how to edit those to your liking.
Put exheader.bin and code.bin from DeathChaos's patch in
After that build a new cpk with Mod Compendium (don't enable compression or extracted files). It will build a data.cpk file so rename it to mod.cpk.
When you're done, put your new mod.cpk in
LumaCFW (3DS Hardware)
Following 3ds.hacks.guide, install LumaCFW on your 3DS. Make sure you enable game patching. Place the modified exheader.bin and code.bin in
sd:/luma/titles/00040000001D7100/ and your new mod.cpk in