I’m having trouble seeing how this would be quicker than just entering a note. You would have to press the key or keys to activate this function, then type in the MIDI number (up to 3 keys) or note name (2 keys).
Using Note Entry, it’s Enter, 5, and press the note.
You can already change notes of one pitch to another using Shift I. I don’t think you can change all notes (of different pitches) to one pitch; but there’s always Lock Duration L to change pitches.