For example, can you make a booty end at just below the bust rather than the waist. Can you make arm mods that turn them into more cat/other animal like hands or make arms that look more likeor . Can you make mods that add multiple arms to the HA like ? I haven't seen anything like this really so I'm not sure if people don't make them or they're not allowed. Subeta items like seem to be ok

You might have a higher chance of getting a reply if you post in the custom wearable discussion forum. Not sure how many CW makers hang out in here to be able to answer your question.

goes higher than the waist and is older than the current body mod rules, so I would assume that would be okay.

I would also assume arm mods of animals would be okay because items that reposition the arms like are allowed.

I don't know for sure about multiple arms, but that could easily just be a popularity thing rather than it not being allowed. In any case, your best answer is probably going to be to file a ticket and get a direct answer from staff. Users probably won't be able to tell you for sure if something is allowed or not unless they know of an item that exists already or they've tried to submit one and got it denied