If a person changes their name, do any copyrights registered to them still apply?
Or at least, as this is the subject in mind, does any software licensed to them still hold the same copyright?
Since the effective date of the US 1976 Copyright act, a copyright notice is not required at all on works published in the US, nor is it required on works published in any other country that adheres to the Berne Convention (which is adhered to by almsot every country in the world at this time). A copyright notice, if present, may specify a pseudonym, a business name, or a form of the author's name other than his or her legal name. The validity of the copyright does not depend on the name in the notice. This is true in all Berne Convention countries.
Even under the 1909 US copyright law, when a notice was required for protection, the exact form of the name used was not important, and pseudonyms and variant forms were permitted, as well as DBA names, which might not be easy to associate with the actual copyright holder. Nor do I know of any other country in which an error in the name in the notice would invalidate the copyright.
Aside from people changing names, a copyright can be sold or otherwise transferred. This does not require changing the copyright notice to reflect the changed ownership of the copyright, although it is often done with new versions or printings. The name on a copyright notice is at best suggestive or helpful; it does not define the owner.
Copyright is held by (natural or legal) persons, not by names. A person continues to own their property when they change their name, including intellectual property such as copyrights. This is a bit jurisdiction-dependent, but even anonymous works are copyright-protected!
The names in a copyright notice are best understood as a reminder that someone holds copyright in the work. For open source software, copyright notices are rarely complete (often just list the project initiator, not all contributors). Names also do not uniquely identify a person, especially if the names are pseudonyms. Together, these problems prevent you from identifying the copyright holders from a copyright notice. If you need to identify the copyright holders, you should also look for other identifying information such as email addresses.