For those who need customs instruments in Dorico and who can’t wait to the next version, I have done this tutorial.
This possible by modifying Dorico and Noteperformer configuration files. This not so difficult but you have to it very carrefully to avoid syntax errors.
English is not my native language. If somebody wants to correct my document, the Libreoffice source is in the zip file.
Note this is for Windows. It is probably the same way on macs with different folders.
tutorial how to add an instrument.zip (507 KB)