Mark/Unmark menu item

Is there an action to Mark or UnMark a menu item without using an If/Then statement?

I understand the 'Select Menu Item' will toggle mark, but is there a way to specify (un)marked.

I don't know of a way for native KM Actions to do this, but you could probably use AppleScript to do it.
However I think that would be more effort than a simple KM IF/THEN Action.