Not possible to unregister it. Once registered, the other person cannot register it on his account.

Thanks for the fast reply, so they wouldn’t even be able to use synapse then? 

That’s not true.

Synapse  has never to do with registering mouse. It’ll work.

Sorry I accidentally clicked the best answer icon. Were you referring to registering for warranty in your first answer? I just want to make sure whoever buys it doesn’t complain that they can’t register it to download drivers, customize and updates etc.

Yes, it only affect the warranty.

You can download and use Synapse 3 without any problem (it’ll automatically download&install drivers).