Change domain for primary site and a few sub-sites only


I have a multisite install with about 25 sites set up as, and so on. I now want to change the domain for my primary site to and I want 3 sub-sites to be, (and so on) but the rest to remain under as they are today.

What is the best practice to achieve this?
I have the plugins "Domain Mapping" and "Multi-Domains for Multisite" installed.

Thank you in advance!