1) Go back to H-lab again and make sure the grabs are actually changed / saved
2) Check Loadout and Prioritize this loadout on option and make sure you are changing the loadout that applies to the character you are fighting
3) Its possible that the grab you selected is not compatible with the target, in which case the game will tries to select a different grab that is most "similar" to the one you selected. For example, maybe you selected a grab that requires target to stripped but the target is still dressed.