The additives for making epoxy coatings less slippery are just fine. Tape off and use them only where you need them if preferred or you will be stuck with the texture. Definitely mix them in with the expoxy.
Just curious, what material are you using that would ever require you to clear coat a new epoxy garage finish? I am not saying it is a bad idea but seems extreme to me? You do know you had better let that floor cure and outgass and vaporize a bit if you do attempt a top coat?
We have been installing professional epoxy garage floors since 2004.
We use a product called Rhino Tooth in the sealer coat. It comes in various grits so you can get the amount of texture you are looking for. Look at www.vbpstore.com/rhino-tooth-non-skid-that-stays-suspended-vial.html