Thanks for help - but I have to try it a third time. 
The Problem is, that a new project - opened as a new one - does not have
the edited PT, but the old one. Only after deleting this old one item, then I can save this edited item in a existing project as a new default.
So it seems to me, that I cant edit an existing default item without deleting it first. I hope, I will be understood. Or I have to sllep a night. Thanks in every case.
Greeting
Bertram