Can I change the instrument within a staff for a few measures and then change it again later in the same staff or can I only have one instrument for the entire length of each staff?
You can use instrument changes to move from pizzicato strings to other types of strings.
The Performance Style Command (http://ntworthy.com/nwc2/help/MNU_ADDPERFORMSTYLE.htm) can also be used. See: Performance Styles (https://forum.noteworthycomposer.com/?topic=5953.msg39024)
Since you are going to be putting
pizz. and
arco on the music anyway, you can get get the instrument change to show that instead of adding extra text objects. After you have the instrument and correct patch number selected, you can change the name of the instrument as well as override placement (prob. want to uncheck "preserve width") and visibility to show it.
!NoteWorthyComposerClip(2.5,Single)
|PerformanceStyle|Style:Legato|Pos:0|Visibility:Never
|Clef|Type:Treble
|Instrument|Name:"Violin"|Patch:40|Trans:0|DynVel:10,30,45,60,75,92,108,127|Pos:10
|Note|Dur:4th|Pos:-5
|Note|Dur:4th|Pos:-4
|Note|Dur:4th|Pos:-3
|Note|Dur:4th|Pos:-2
|Bar
|Instrument|Name:"pizz."|Patch:45|Trans:0|DynVel:10,30,45,60,75,92,108,127|Pos:8|Visibility:Always
|Note|Dur:4th|Pos:-5
|Note|Dur:4th|Pos:-4
|Note|Dur:4th|Pos:-3
|Note|Dur:4th|Pos:-2
|Bar
|Instrument|Name:"arco"|Patch:40|Trans:0|DynVel:10,30,45,60,75,92,108,127|Pos:8|Visibility:Always
|Note|Dur:4th|Pos:-5
|Note|Dur:4th|Pos:-4
|Note|Dur:4th|Pos:-3
|Note|Dur:4th|Pos:-2
!NoteWorthyComposerClip-End
HTH
Unless you want
pizz. and
arco, in which case you are back to using text.