Just chipping in with an alternative solution to the “move the label” request. What I do is go into Edit Names, then simply add a return or enter at the end of the instrument name.
You can’t actually see anything in the entry area when you do this, but the invisible character is there and Dorico will align the (now) two-line label centrally on the stave:
Quick to do/undo, and if you type the return character before the name, you can move the label down instead.
Since you’ll likely need a graphics frame for the ambitus of each part, you could also just turn off staff labels entirely, but still set an indent on the first system, and include the staff names in whatever graphics you create for your ambitus staves. I’ve had splendid results exporting graphics from Dorico to vector form — you could design the ambiti in Dorico, export them, crop and resize them as necessary, add staff labels if you choose, and pop each finished graphic into its own graphic frame.
Thank you all for the support. Rob_KB’s solution seems like a very interesting solution to me, but I haven’t been able to put it into practice.
I did it, thank you very much!