There are some restrictions when changing the process web services between process versions.
If a web service is shared by two versions of a process (same endpoint address), it must have the same WSDL definition (same portType, same binding...) in the two versions.
A new version of a process can add/remove web services (if receive activities are added, removed), as long as they use a separate portType.
A web service cannot be shared by two different processes (processes with different names).