I intend to sign up with a web hosting that allows unlimited addon domains. Is there any way I can assign different IP to each addon domain that I include in the hosting?
It is *technically* possible, but you have to find out from your host if it is included in your package, or whether there are additional costs. They may have limited allocations themselves.
Impossible for you anyway, as suggested I would ask your host, don't go looking in cpanel you won't find anything.