I’ve noticed that transposing a section of music the key signature does not change, though if the signature is a part of the section I have the option of transposing it.
How do I transpose from C major to C minor? If I just change the signature I now have natural signs in front of each E, A, and B. I don’t see how I would transpose just those three pitches.
Select All, filter for Notes and Chords. Shift+I to open the notes and intervals popover, then e=eb,a=ab,b=bb and Enter.
Wait… does that do all those notes in the flow!?
All the selected notes, yes.
You learn something new every day, though I don’t use the intervals popover very much.
I’ve just removed my original reply because yours is better.
Hi @bellist, besides the useful solution by @asherber, as an alternative there is also the Map Scale functionality (menu Write>Transform>Map Scale…), which can be handy in other scenarios too, depending on your needs:
Workflow:
Thanks for pointing it out.. I’ll have to play with it.
To add to the very good suggestions already given here, the note tool popover (Shift+I) also lets you enter syntax like c M to c m — for the minor scale, that gives you the harmonic one, here with B naturals.
(credit to @Janus who mentioned this in a thread, a couple of months ago)
And if you want the B flats: c M to c nat m
I bookmarked that post and came here to say the same thing 
Shift+I can be really powerful.
There is one more solution: Make your selection, then open the interval popover and write “snap cmin”.
I find that one to be unreliable as sometimes the notes snap the wrong way! It would need to be snap c m down else E might snap to F rather than Eb (I know it shouldn’t but it does!)
Unfortunately, after testing again, you are right! Tried out for example a C major scale to “snap” to g minor, which results in c d eb f# g a c c. No b.
Obviously this function needs to be revised.
Meanwhile the the note tools popover – not just intervals – is my favorite 
I rest my case 
These are both great functions that I hadn’t explored!
I believe this popover started out as an Intervals popover – hence the Shift+I – and later changed to Note Tools as it added more functionality. In my head, I still find it useful to call it Intervals, to correspond with the key command, even though I know it does much more!
