I chickened out.
I have a leak in the pipe that feeds the spill over spa when in pool mode. Rather than try to fix it, I capped it in the spa and am re-plumbing to direct that flow to the spa jets. I'm able to do it all above ground at the equipment pad. Only requires some PVC pipe, fittings and a check valve. My project for the weekend.
Only loss is I can no longer have a fountain effect in the spa. But I never used it anyway because I thought it looked silly, required a pipe in the middle of the spa, and raised the pH like crazy.