Move iMessages between accounts
Short Answer: No

Longer Answer:
Apple does not support and even don't know how to merge 2 Apple IDs/Account. But on your local iPhone you can hold all the Data if you only switch the iMessage ID afaik. iMessages are only hold for 14 Days in the Apple Account and are not/nerver longer stored at Apple (claims Apple) 

So moving iMessages to another account without Dataloss - No
Keep old Messages on the same Phone (or Backup) - Yes