Changing note durations without affecting subsequent notes

I want to change the duration of several consecutive 16ths to 32nds. I know I can do this, but when I follow the instructions linked below, subsequent notes are shifted to earlier in the score by the cumulative time I shortened the group of 16ths. How can I leave subsequent notes and measures untouched? I would like rests to be inserted right after the group I shorted to match the exact amount by which I shortened it.

Second, but related question: What if I want to take six consecutive 16ths and convert them to a 6:4 tuple (or any other arbitrary tuple)? Is there a way to do that?

Probably not necessary, but here is an image of the music I am editing:

Add a stop bar (shift-alt-I) - the strange red vertical line appears.

Select the first, invoke the tuplet popover ; and enter 6:4x

3 Likes