Changing a Trainer Class' associated Battle Theme in Black 2

[Estreth]

Hello folks, so I am completely stuck on this matter and would greatly appreciate some assistance in this field.

So I've added some of the Gen 1-4 Gym Leaders during the main campaign of my Black 2 Romhack as a little side quest and I would love to make it so that their respective PWT Gym Leader themes play during their battle but I am completely flummoxed as to how to do this. I do know the basics and have made some Hex Edits to the Rom already with HMs able to be deleted and new TMs but I have no idea how I can do this for assigning different battle themes to different Trainer classes (so the Kanto Leaders would use the Kanto PWT Gym Leader theme etc)

What files to I need to extract? Which overlay (if any) do I need to search for and is there a resource that lines up Trainer Classes with their hex codes (as well as which hex code correlates to which battle theme) and which hex's do I need to change around so that it all lines up?

Thank you for your time!