Persona Q is a spinoff title in the Persona franchise. Developed as a joint collaboration between Atlus's Persona team and the Etrian Odyssey team. It takes place between Persona 3 and Persona 4, featuring the nearly complete cast of playable characters from each. 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.
Persona Q has a sequel called Persona Q2 that was released November 28, 2018.
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).
Extract the contents of your 3DS rom using DotNet3DSToolkit. Replace exheader.bin and code.bin in your extracted ROM with the ones from the mod.cpk patch. Place the new mod.cpk in the same directory as the data.cpk and rebuild.
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/0004000000123400/ and your new mod.cpk in