Microsoft is notifying Remix 3D Preview users that their profiles will soon merge with Xbox Live profiles. The message is being delivered to users via email, and the move itself will occur on April 30th, 2017.
According to the email, (seen above) the merge means that users will have just have one profile, tied to a Microsoft Account, which can be used for Remix 3D and Xbox experiences. So, if you already have an Xbox Live profile associated with your Microsoft Account, you’ll see your existing gamertag and pic on Remix 3D the next time you sign on. If you don't already have an Xbox Live profile, you'll need to choose a new profile name ("gamertag") and pic ("gamerpic",) and you'll be guided the next time you sign in.
You can go to Remix3D.com anytime between now and April 30th, 2017 to create a new name for your Remix 3D profile, and After April 30th, 2017, a new profile will be made for you, so you won't lose your stuff from the Remix 3D preview. In the instance that you don't like the new profile that has been made for you, you can change it once for free by going to Remix3D.com > My stuff > Edit profile.