Is anyone familiar with how ENS handles the creation of subdomains?

Not sure if this is the best place for this. I'm trying to wrap my head around an implementation detail of ENS around the creation of subdomains; it seems like if you own an ENS domain you can create subdomains yourself, but if you want to allow other people to claim ENS subdomains you need to relinquish control of the ENS domain to a registrar contract. From documentation I've seen, this seems to be permanent. My question is, does this step HAVE to be permanent or is this just an implementation detail of the registrar smart contract? Would it be possible to create conditions that would enable the owner to retrieve ownership of the ENS domain from the smart contract?