Adding/deleting/upgrading licenses could/will essentially change what your installation is capable of, so it's better to be safe....
The Admin Guide for 6.5 (UNIX) is a bit confusing in that, whether talking about adding or deleting licenses, it gives the following warning:
"Note: Restart all the NetBackup utilities (including NetBackup-Java Administration Console) after deleting the license keys."
Whereas, the same section in the Admin Guide for 6.5 (Windows) has no mention of restarting services!
Further, there are TechNotes that state if the licenses were added/deleted via the Admin Console then only the Admin Console needs restarting!
So unless it can be clarified to the contrary, & to be safe, I would.
You could of course go the opposite way & not restart services & see if things worked as expected!