Animating inside a motion clip

Hello

I have a simple character animation (arms going up) that I made into a motion clip and I’ve put two copies in the TL, one moving forward and one moving backward so I can ping pong the animation.
Now I realize I need to have the character to an additional move (spin on himself), but only in the first motion clip.  Is there a way to edit the motion inside the motion clip but keep another motion clip identical?
Maybe I need to make a copy of the original animation and just edit that?

Thanks