I've done the workflow you describe personally on my Macs. The deactivation is probably not critical but it definitely won't hurt and a good idea. Our licensing technology has improved in that if you attempt to activate on too many computers it now gives the end user an option to de-activate themselves versus having to call into support for assistance. I probably would also recommend uninstalling and then reinstalling on the new system. Reason being the installation of some products looks at the current system configuration when installing, using the migration assistant circumvents this occuring and could potentially cause issues. I'd also make sure your permissions are in order after the migration.