Finale Forum

The piece begins with all voices singing in unison; the single vocal staff is designated "All." Halfway through, the ladies and men break into different parts. There is a new vocal staff mid-piece that is now called "Men" but haven't figured out how to rename the "All" staff "Ladies" at that point in the song.

Is this possible?

The easiest way is probably by using a staff style applied to the first measure of the systems where needed.

Zuill

I must be doing it wrong.

Staff Tool/selecting the left-most square, closest to staff name.
Staff/Define Staff Styles.
Changing the Full Staff Name and the Abbreviated Staff Name. Hit Okay.

Perhaps some other preference is not allowing the staff name to change?

Having Defined the style, you need to apply it.