Hi, I've found this post while looking into how to modify my Pokemon White Romhack.
I think the "Frost Gen 5 Editor" tool might be the solution to your problems. With it, you can edit trainers—specifically by assigning them a particular trainer class—which changes the battle music to match the chosen class. I haven't verified this for the specific classes in question, but I guess that assigning a Gym Leader their corresponding trainer class from the PWT should trigger their specific music.
For my part, I am looking to—among other things—make HMs deletable and change the moves contained in certain TMs, so could you share how you made these changes ? I assume it involves hexadecimal data, but I’m struggling to figure out how to make precise edits (like vendor inventories—I read that this is located in the "overlay9_21" file, but I can't seem to find the specified coordinates; perhaps because I'm using a French ROM, though I'm not sure).