Is there already a way of respelling music, meaning leaving the rhythm and changing the note names?

Yes, it’s called “Lock to Duration” and can be found in the notes toolbox.

Thanks Ianpartridge.

I have a problem with “Lock a duration” : I can’t enter chords with my midi keyboard, only solo notes. It’s maybe a bug… ??

Yes, I’m afraid lock mode and MIDI input don’t currently play nicely together. I hope this will be addressed for the next update. Sorry for the inconvenience.