Would it be possible to add an action to call a named system service similar to apps like PopClip and TextSoap?
Both seem to work by specifying either the name of the service as it appears in the Settings app or in the Services menu, and then they pass some text to it.
Service actions — PopClip Developer (I can't find the docs for this for TextSoap, but it works pretty much the same way.)
I saw the post at How to open links in Safari from Chrome or how to call a mac os service ? - #3 by Andreas_Hegenberg, which recommends using menu-item triggers or keyboard shortcuts
One advantage of not relying on menu triggers or keyboard shortcut would be that it looks like you can call an installed service without it being enabled in the Services menu (which can get quite crowded) and without an assigned shortcut.