Board Thread:Bug Reports/@comment-75.22.138.225-20160902233332/@comment-25330335-20160907184202

Well, the original playerdata is still there, you just aren't using it. The solution below is completely theoretical, and by no means has been tested. BACK UP YOUR WORLD before you move to do any of these steps.

I think that if you rename the playerdata file with your new UUID then you should be able to use your old playerdata. Find your new UUID using this tool. Then find your playerdata file in the world folder (make absolutely sure you've backed up the world). Rename the (hopefully) only file in that folder to the new UUID. If there are more than one, find your old UUID and rename that file. Then try it.