You can only have one active forum at a time. So if you want to change domain or something, you just delete the old install and then update your customer details.
Yes, you can change your URL as many times as is required through the Customer Area. The only rule is that at any one time it must not be installed on more than one publicly available URL. You can, however, have a second copy installed which must be password protected and only used for testing and development purposes.