Authentication is only done at the time of enrollment with iOS, so if you're talking about changing the settings in Systems Manager > General > End User Authentication then you'll notice that Systems Manager > Owners will populate when new users enroll
However, if you are talking about setting up Federation in Apple Business Manager / Apple School Manager, and are using shared iPad, then you may notice a few changes on the device, and you'll have to ensure that you go to Systems Manager > Overview and sync Apple School Manager to get the new users
Without any more detail, I can't offer any more information
BUT, long story short: You won't have to reset / re-enroll devices
