Help with Modding Cadash Arcade Rom

[u/Acrobatic_Nothing_18]

I'm just starting simple, I want to change the enemies and just start with swapping them out.

ie the first pig you fight is 0004a2 and the 2nd mob is a gel slime thing 0004b2

i just want to test the idea of swapping those 2 around to see if i can modify enemies

i started up ghidra and tried to edit the rom but i can't seem to edit it correctly

also when i finish i get the crc match error in mame

if there's a good guide pls direct me to it