Windows 7, Finale 26. (I also have posted this on the Finale side, in case that is more appropriate.)

Well, just when I thought I understood changing instrumentation mid-score with a custom Expression, I am, again, flummoxed :-0
Yes,, flummoxed, I say ;-)

Below are screenshots to help with what I am trying to do.
I have a Grand Staff (piano, two staves) and wish be able to assign separate dynamics each--but NOT with Layers, because I often use all four.

I have successfully done so for the entire work, but I want to be able to do mid-score, in any given place, and then return.

So, to begin, each staff would be Channel one, but maybe in Bar 3 I want to have the lower staff play "p" (soft) but the upper staff continue at "f" (loud).
How can I do this--assuming it is possible?

Thank you, in advance.
:-)
Vanessa