[Wendy Cutler]

You could use the custom group or the custom fields for instruments and arrangements (or reuse one of the existing groups that you do not need for its original purpose)

Thank you, @itsme. I might be misunderstanding, but I think these fields all have fixed values, from which one selects a value. The arrangements are text instructions, like "Violins in second A, accordion in second time; all shout 'hey' on third time". I don't think fields work for that kind of thing, where there isn't any standard selection to be made. 

That's helpful to know to look for the field delimiter for the output.