Is there a faster way to extend the note with, for example, one 8th note? I mean, with 3 voicing is still manageable, but sometimes there are 15 voices at the same time …
Yes. Select the notes and press Ctrl-Shift-Right arrow to lengthen their durations. First, set your rhythmic grid to 8th notes.
Yes, thx!!!
but I think you meant option-shift and not control-shift 
thx
something goes wrong, the whole piece moves with it.
What is happening?
Sorry! I’ve done it for so long that I do it by feel and had totally forgotten which keys they were!
You have insert mode turned on. Press “I.”
no problem !! and yessss that’s much better! thx