There in v1.3.1 there is a option to add a always inverted switch. So this simple mod you can add it if you want.
The first Inverted output version, I tired the idea with a separate Inverted CV Jack.
But as someone pointed out that the way the circuit works if you tweak of offset knob it wont just effect the the first CV jack with the offset knob, but also effect the Inverted output switching polarity too which kind of defeats the propose of it being a always Inverted Output.
I am looking into designing one that has a Always Inverted CV output. But it would require more work to function properly and a full redesign with 2xTL074. Tomas Henry MFOS Quad DC Modulation Mixer has something very Similar and is a interesting read if you want to learn about Op amp Mixers.