Moog Theremini | Is there a way to control multiple external parameters with the one CV Out on my Theremini?

Yes. 

By initially connecting the TS cable from the CV OUT on the Theremini to a mult input, you can subsequently route that signal to various different CV Input parameters. 

For instance, if you link the multed signal from the Theremini’s CV OUT to both the 1V/OCT & VCF CUTOFF inputs of a Mother-32, you can control both the pitch & filter at the same time with the Theremini using a wave of your hand.