I think you can switch back to non-grouped owned region. I seem to remember you can but when I did it for another person I was an admin using God powers. So if you can't switch back, you can have an admin do it for you.
I do not remember how this was handled by the viewer prior to me being a grid admin. Now that I am no longer a grid admin, I would have expected that regions that are grouped owned and have the proper group permissions to edit the region settings would be able to modify the Region/estate settings. Could this be a grid issue vs a viewer issue? I'll have to test it on Firestorm to be sure.
Thanks,
Geoff