Once you have synced the Wii Fit Meter to your free copy of Wii Fit U, the video game is yours to keep and no, you will not have to create another profile.
And if/when you do get another Wii Fit Meter, if you have updated the game to the latest version, it should automatically give you the "Ready to Receive fit Meter data", so just use the "Start without transferring" option and that will take you to your Mii Character and select the "User Settings".
And at the bottom of this new screen, now click on "Fit Meter", which you then use the "Delete Registration" option.
http://wiifitu.nintendo.com/getting-started/
And once that is done, just go through the process of syncing your new Wii Fit Meter.