I work at a registrar and as far I know there are no protocols. We are an intermediary between the registry and registrant (in those TLDs which have a registry/registrar/registrant model), but the business relations involved are a bit more complex. The registrar's job is mostly set to only handle the technical and billing aspect, while the legal relationship is between the registry and registrant. Who owns a domain and which registrar handled the billing and technical aspects is a legal decision which is outside the control of the registrar.
The variation between TLD and TLD is massive. Practically all ccTLDs have their own home made rules and more often than not their own technical solutions to match. A big reason why the more exotic ccTLD's can cost a lot of money is the hoops that registrars need to jump through, both legal and technical, and the "workarounds" for both.
There are even ccTLDs like .af (afghanistan) where the root zonefile is edited by hand for every new domain, in this case by some persons at the "ministry of communications" in kabul.
The variation between TLD and TLD is massive. Practically all ccTLDs have their own home made rules and more often than not their own technical solutions to match. A big reason why the more exotic ccTLD's can cost a lot of money is the hoops that registrars need to jump through, both legal and technical, and the "workarounds" for both.