Changing account domain to parked domain

[Babylon]

Situation: I have an account set up with domain1.com. domain2.com is parked on this account, and there are email accounts set up under the domain (ie: user@domain2.com, user2@domain2.com, [...]).

domain1.com is now due to expire and will not be getting renewed. domain2.com needs to become the account's primary domain vs just being a parked domain. However, I can't just edit the account in WHM as trying to change domain1.com to domain2.com is gives an error stating the domain is already setup.

If I was to unpark domain2.com first, all the email accounts will get hosed. So what's the best approach?