Can Mac Messages connect to more than one apple id?
You can set up two iCloud accounts on a mac.
In System Preferences you can go to Internet Accounts, there you can see al your accounts, and you can easily add another iCloud account.

You can then select what you would like to use with the new iCloud account, keep in mind though that only one of the iCloud accounts can be used for photo stream at a time.
This answer on the apple support community site also explains it.