Wie kann ich in einer Einzelstimme mit mehreren Instrumenten die Instrumentennamen auf der gesamten ersten Seite vollständig anzeigen lassen und auf den Folgeseiten nur abgekürzt?
Welcome to the forum, @Max90er
Assuming you speak about staff labels, and you have only one system in the first page, have a look at Layout Options[1] > Staves and Systems > Staff Labels
Edit: according to (the translation of) your title, you seem to have more than one system in the first page. If so, insert a system break on systems 2, 3… (in the first page), select the signpost and in the properties, activate “Staff labels” and choose “Full”
Ctrl(Cmd)+Shift+L or Library > Layout Options ↩︎
Thank you so much for your quick response. The problem is, that I have more systems on the first page cause it’s a piano reduction with singers. The Staff labels in my layout options are set like in your screenshot. Do you have any other idea, how I can sho the full name on the whole list page?
I was editing my answer while you were posting, see my edit above!
Thank you. I try! 
Thanks for help. You solved it!