\cadenzaOn and \cadenzaOff do exactly what I am looking for; I apologize for not finding those before asking the list.
As far as "turning off" and the other parts, I've decided to put the cadenza in the other parts as a CueVoice. Once I get the score completed I may look at trying to turn the parts off for the cadenza, but it's not a top priority for me.
There is also an "Alternative Ending" to consider, but that's about 32 measures in the future.
I would like to say how much FUN it is to use Lilypond and Frescobaldi. I have friends using expensive commercial packages and I think my results are every bit as beautiful as theirs, if not more so (which may be, in part, of the effort I am putting into crafting the score). And the support on this list is far beyond anything I could have expected. Thanks to all for your hard work and dedication.
--greg