I should add this.
Adding on a group-ex certification would probably be relatively easy study-wise if you are already a certified personal trainer. The anatomy / physiology is the same, and that seems to be a piece that takes people some time to learn. The biggest topics that are different are:
1) Class design (that’s only two words but it’s a lot of education)
3) Class management (verbal cuing, visual cueing, use of music if you’re using any)