I think you mean the Power CMS Builder Extension, is that right?
With the Power CMS Builder extension, There is one serial number for the extension that is also used to activate the Power CMS Installation on the web site.
It can be used on unlimited sites, but will need to be activated for each one.
The activation is based on domain name, so nothing will happen is the site changes server, but retains the name domain name.
if then site changes domain names, then the CMS will need to be reactivated.