I'm trying to give a unit capability to scale cliffs. But when I change its mover pathing mode to scaler, it doesn't just affect that one unit but all ground units, including the enemies. Is there a way to make it so that only the unit of my choosing can scale cliffs?
You must duplicate the "Ground" mover. Assign your new copy of ground to the unit you want scaling cliffs. The "Ground" mover is used for almost all ground units, and so editing it affects a lot of units.
Go to the unit, and find the Mover data item (Movement - Mover?) and change it to your personal mover. If your duplicated mover does not appear in the list, make sure it is not set as "Use as default" in the menu that appears when you double-click on it in the list of all movers. If it still doesn't appear, change it's ID in the double-click menu to something else.