I would never use those in the Ruler to change margins. The vertical ruler displays on the left side of the page.
I guess if you are changing it for the entire document it should be OK. I prefer to use the layout dialog.
Changing top and bottom margins for part of a document should insert a next page section break.


In the Windows version the margin shows in a different color. If I move my mouse pointer over that border it turns into a double-end arrow to allow moving.