turn \RemoveEmptyStaffContext on and off?

[Kieren MacMillan]

[ Lilypond 2.9.7 ]

Hello, all!

Just wondering if \RemoveEmptyStaffContext can be turned on and off  
at will? [The only thing I know about is \context  
{ \RemoveEmptyStaffContext}, which seems to be "global" for the  
entire duration of the \score.]

The situation I find myself in is this...

The conductor I'm working with doesn't *really* like Frenched scores  
-- if an instrument is ever going to play in a given movement, he  
would like it to appear (with rests) in all systems for the entire  
movement. The exception we've already run into is that there is a  
large section of one movement where the two vocalists sing cappella  
for about seven systems, and then the band comes in for the last few  
measures. We'd like to hide the 8 empty staves (4 for the linear  
instruments, plus 2 each for piano and reduction) if possible.

In other words, what I would like to do is French score the movement  
only leading up to the system containing the entrance of the  
instrumentalists, then *NOT* have the score Frenched for the  
remainder of the movement.

What's the easiest way to do this?

Can I override some Score variable at "just the right moment"?

Or do I need to explicitly code a \startStaff in each instrument/ 
Staff? If I do, is there an automatic way to ensure that all of those  
started staves extend back to the beginning of the system they start  
in (because that particular measure might not be at the beginning of  
the system, depending on the layout), or do I have to change that for  
each edition/layout?


Thanks,
Kieren.