This MuseScore 3.x plugin, largely based on the elegant code of the New Retrograde plugin, copies your selection (1 staff, 1 voice) to an adjacent score, prefilled with the desired rhythms in rests. The destination score has to have a similar general outlay, and enough measures to accomadate all the notes, but differences in time signature are OK (see the attached SchubertTest and Respell demo files).
Should be useful to untriplet/retriplet a sequence of triplets or tuplets. For an individual tuplet you can also use the Duration Editor plugin.
Try it yourself: open the SchubertTest file and then the Respell demo file. The plugin uses cmd (“next-score”) so this file has to be adjacent. Make a selection in the test file and run the plugin from the Plugin Creator window so that you can see error messages. Please report issues in the forum.
“Juste pour rigoler”, as the French would say, I also tried a more complex selection & desired rhythms: