[1.12.2] Editing Rabbit Spawn Rules

So with my mod, I'm attempting to make the Rabbit spawn as the Killer Rabbit in the custom dimension that was created, unfortunately the first method I tried, directly editing the code in a way that, in theory would work, ended up in an immediate crash, but when I reloaded the world w/o said code, the KR had actually successfully spawned. I then tried to find safer solutions, but they either crashed the game upon initializing, or just spawn regular old harmless fuzzballs....can anyone help me with this pickle I'm in? I also have a Discord, ChaosDog#1893, but try to notify me in advance if you are going to add me as I'm kinda in a paranoid state of mind atm for other reasons.