I'm in the midst of writing a piece which has an organ part which may require stop changes during the performance, possibly mid-note (with the resultant tonal shifts). Searching the web I've tried to find out how to do this but have come up dry. What are the accepted practices for scoring stop changes?
You simply write the desired stops above the staff: something like
Gt: + 4' Reed or
Sw/Ped off or
Soft Fl. 4' solo. If you want to do this while notes are held, then you need perhaps a special symbol like an arrow or star along with the text, with a note at the beginning of the score explaining what it means.
In Cesar Franck's Grand piece symphonique there are several places where the composer asks the organist to add all the reeds while holding a chord.