Something which may be useful in this context would be to show how to create new shortcuts for Scrivener.
Apple has some helpful documentation online on the subject
But there are some things which are not said explicitly there. For example, a sub-menu will work as well, as long as there is no other sub-menu in the application which has the same name. If you need a menu which ends with three periods... , i.e. an elipsis, then you often need to use option-semicolon for the elipsis otherwise the short cut will not work.
I use subscript and superscript a lot, so I created one which looks as follows.
To see a bigger picture, click this
It would be nice with the ability to set back to "Use Default" for the baseline, but then we would need the menu item to have a unique name. As it is now the Ligature menu (and others) have a menu called "Use Default", so you can't use that. If the menu instead was called "Use Baseline Default" then we could set it. (But that I suppose is a feature request which should be entered on the Wishlist.