Hello Richard (and or whomever gets this email, I'm not sure who the recipients are),
Something that you may, or may not be interested in adding, eventually:
If someone was writing with counterpoint in mind, adding intervals
easily (good for beginners like me who are learning music theory
alongside using Denemo) to the staff above (or below) the Cantus Firmus
could be achieved with something like (with cursor on a note on lower
staff and staff above blank, in this case):