Presently I have to do two operations for that: switch the note to to-do (and, on Windows desktop version, sometimes I have to search for the note in the Notes List, even if I have the note text open in the editor); then set the alarm.
I propose merging "Switch between note and to-do type" and "Set alarm" operations to the single "set alarm". I.e. when I edit the note, I should be able to simply click the (grayed) bell toolbar icon (on Windows version) or select "Set Alarm" (on Android version). That will automatically convert the note to to-do and invoke the Set Alarm popup.
In the Set Alarm popup we'll need one more button after "Clear alarm": "Switch from to-do into note".