How to limit user chosing flair?

[Heliosurge (Dan DeMontmorency)]

You might want to consider this theme component.

It gives Trust Level flairs and still allows other flairs.

Trust-Level Avatar Flair

This theme component allows an admin to add flair to user avatars based on the user’s trust level. Trust level flair displays anywhere on the site that you would normally see group flair. There are a few theme settings to adjust the position of the flair in relation to the avatar. Basic Examples (with group flair in place) [examples] There is also a bottom-right position that will either replace group flair or be replaced by group flair depending on how you set the “group flair always on top” …

Otherwise I think you can turn off choosing flairs by disabling choosing primary group.