Oops! Forgot to answer your question. I understand a library file to be one that saves all your settings, viz. articulations, expressions and lines. I would save a library only if I added a number ...
Whenever I try to write for an instrument, like Castanets, Didgeridoo or Cajon, Finale brings up the following notice. "The selected document Style does notinclude the Percussion Layout requiredby ...
There are a number of apps you can use for backups to avoid such issues in the future; but, as far as I know, you cannot simply "backup," "Copy" or even "clone" as they will not faithfully rebuild ...
If the part is played rapidly, maybe write it as an arpeggiated chord, or two arpeggiated chords (wavy vertical line in Articulations Tool, which can be customized, say, bottom note at -512 to 0 to...