Who is able to make changes to a domain?
The Joker.com login account which has been used to register a domain is able to modify all aspects of this domain afterwards.
Additionally, permissions ('roles') may be granted to other Joker.com accounts as an option.
Please check here to find out more about those grants and 'roles'.
Also, the person who represents the "registrant contact name" in the Whois data of a domain is authorized to request changes to a domain.