According to the Envato License Terms, it's not possible to use one of the Standard Licenses on multiple clients or jobs. In a nutshell, 1 license = 1 domain:

• Envato Market Regular License

The only time a license could be requested to be reset is if you need to move a staging site to a live domain, but even in this instance, you will need to remove the staging once it has been migrated. If you want to keep a staging site indefinitely, this would require a dedicated license. 

If you want to avoid problems when registering a staging site please follow these options:

• A) Create the staging website on a subdomain of the final website staging.clientname.com and clientname.com (as the final website);
• B) Create all the staging websites on your subdomain and register all of these with the same Purchase Code clientname1.mywebsite.com, clientname2.mywebsite.com and then use the dedicated Purchase Code to register the final domain.

In a nutshell, a license can be used on a domain, if you change the domain you may have problems with registration. If you are having trouble with the migration or registration please follow:

• Migrate a Purchase Code