The only thing that is different is, that the default WhatsApp Apps are asking the phone for the number every start (or even while the App runs) so when you change your SIM you would need to register a new Account for this number and you can't use your old Account anymore
-> If you want to try: Just do the registration-process as described by me here again but with a different password. It should work (if you do this please save the XML's you get as answer and if there are differences to the first registration please let us know)