If you aren't using Opus on the machine that is just sharing the Opus program files, there's no need to enter a licence on that machine. Uninstall to remove the licence, then just run the installer when you want to update the shared files, but don't run the program itself.
As long as Explorer Replacement isn't turned on, not having a licence installed won't cause a problem if the program is installed but doesn't get run.
If you want to add an extra licence:
The online ordering system only supports one, two or five install licences but if you want three, four or any other number just drop us a line to sales@gpsoft.com.au and we’ll sort you out.
(From Common purchasing, upgrading and licensing questions )