I did not know this was possible.
Create staff with zero or more stavelines recept.
- Create new empty project
- Add player with instrument you will not use. (for me Theremin)
- In Setup - Players => Edit names to … and Save as default for instrument
- In Windows edit …user\AppData\Roaming\Steinberg\Dorico 3.5\userlibrary.xml
- Find and edit < numStaveLines> x< numStaveLines > (x can be 0 or more)
- Restart dorico (don’t know if this step is needed)
- Create new project with theremin as player with a staff of x lines.