For the 2 people (if that) who really care and want to know what I am talking about, I am making an axolotl mod that adds more variants. "But, Joe, just retexture More Axolotl Variants Mod like you have done three-and-a-half times already." No, it only adds 10 variants, and all with wierd rarities. I don't care how rare the colors are IRL, I just want more variation. So the weights for mine will be whatever vanilla axolotls are. Except the wild green one. That one will be 1.5 to 2x vanilla axolotl spawn rate. Also, I want at least 15 variants. "Well, just install more axolotls and retexture it's axolotls too." Now you are just being picky. I want more control over my mod than that, plus, once I understand how Fabric works, I can make more mods. So, maybe you can expect some simple vanilla+ mods from me in the near future.

I looked, and less of the entity data is in the datapack folder, so no, not without some legendary hacking skills. Besides, even with the hacking skills, you might notice that datapack mods have huge limitations and you immersion is ruined one way or another. The fabric mod path allows me to make it super lightweight and do exactly what I want.