I have a bunch of pets with TC spaces they'll probably never use. It would be nice to transfer them to other pets that might need them. But maybe make it so that you can't go lower than the default three so everyone doesn't start milking pets for all their TC spaces.

I can't remember exactly the source, but it have been suggested before and not approved unfortunately.

I think the rationale is that TC spaces are a part of the pet itself just like stats, and hence it could not be transferred.

From [topic not found] which is the same suggestion only made back in 2012:

That was the only staff response I could find on the subject. It has been suggested a few times since 2012 with various levels of support and disagreement.