One of my clients I set up with a multisite (lets cool it coolstuff.org) has another organizations domain mapped to a subsite. This was done in maybe 2014 using the old Domain Mapping plugin, which is no longer necessary.
The organization with the mapped domain opted to register a new one that is shorter and is asking how to update the mapping. I’ve added the new domain to their cpanel, which set up the A/C records, and when they are ready, will tell them to change the nameserver on their domain registrar. Once that is done I will change the site_url value in their Multisite settings
The one thing is fuzzy is that before I think we had them use the nameserver for the account domain, something like ns1.coolstuff.org and ns2.coolstuff.org - is that still right, or can they use the normal ns1/ns2.reclaimhosting.com
Fuzzy is the memory.