I assume you are talking about the spacing between power/ground fingers bonded to the same ring. If that is the case, I would suggest using the same net finger-finger spacing rule inside of Constraint Manager.
You can create a same net spacing constraint set (Maybe call it "PG_NETS" or something). Then, change the finger to finger spacing value for that. If you wanted the same spacing between fingers on any of the rings in your design, you could add all those nets to the same same net spacing constraint set that you created.