Well, either the same parm on all 4 operators for some parms, or envelope rate xor level settings for a single operator, but not arbitrary parms. But it is indeed 4 sliders, and not just 2 or 1.

Interestingly Yamaha documents the CC codes for the Reface DX, so you can use an external controller with knobs such as an Akai to go wild with altering the patch while you play.

I’ve only done a little bit of this, but here’s a video where the guy is all over it 12 minutes or so in https://youtu.be/Xt-tmIMCxTk