Yes, you can hide empty staves: look at Layout Options > Vertical Spacing.
If your changes in staffing occur in ‘sections’, you could use separate flows with different Players for each section. If the changes occur mid-way through the music, you’ll want a different approach.
With Solo Players, you can add an extra staff at any point - even in the middle of a system. With Section Players, you can create divisi passages, where one staff splits into two or more, even Solo and ‘the rest’.
One possibility it to use SATB players, and just use the S and B for the choir reduction, hiding the empty Alto and Bass staves. Then just use different voices for each part, and create the Solo S with one of the techniques above. Or just have a Player and hide the empty staves!
I wouldn’t use condensing, as that’s really for instrumental parts.