While discussing archiving limitations in macOS Sierra Messages.app vs. the iOS equivalent (iOS allows you to automatically delete messages over 1 month or 1 year old), another IT friend of mine wrote up a guide on how to transfer messages between two accounts.
Messages are stored in
~/Library/Messages, but the step by step guide below helps with some of the oddities to ensure you can transfer the folder correctly.
This guide is for those who want to transfer their Messages history across to a fresh user account. The instructions here assume the new account is on the same Mac, but you can probably modify this easily enough for moving your Messages history to a different Mac. Tested under Sierra.
Before proceeding, keep in mind common sense: back up your data, and proceed at your own risk.
1. First, quit Messages on the new account.
2. Open Messages on the old account and make sure all the latest messages have been received.
3. Now quit Messages on the old account.
4. Delete the folder
5. Copy the folder
/Users/newAccount/Library/ . I recommend using
sudo cp -r for this step to make sure everything copies properly.
6. In the new account, in Finder, open the Get Info panel for the newly-copied Messages folder. Unlock the permissions section with the padlock in the bottom corner.
7. Make sure that the new account has Read & Write permissions to the Messages folder.
8. Make the new account owner of the Messages folder (via the gear button).
9. Delete all other entities in the permissions section so all that’s left is the new account with Read & Write permissions and everyone with No Access.
10. Again, using the gear button, Apply changes to enclosed items. This step may take a few minutes, depending on how much history you’re keeping.
11. Reboot your Mac. This is important because otherwise Messages will NOT pick up the folder.
12. When you log back in, try opening Messages. The old conversation history should appear.