couldn’t figure out how to Add an action not already in the Name column
Well, you can’t add any actions in the Shortcut Mapper. They are what they are. If you can’t find what you are looking for exactly, perhaps you can combine a sequence of several actions into a macro and then assign that macro your desired keycombination. Have a look at the Macros menu and its commands, try some things, and if you can’t figure it out and need more help, post here again.