I believe it can be done with a formula device to discretize the cutoff steps according to a preset scale and periodic update frequency.
I have not done this exactly yet, but very similar things, with formula devices.
For one thing this code may be useful for you: https://forum.renoise.com/t/effect-presets-tuned-keytracked-effects-formulas-doofers-ktrk-1-1/ - these are keytracker tuning formula device presets, they allow certain renoise native effects to be tuned to a keytracker…also all the native analog/digital track effect filters’ cutoffs…
The other code I had already done was tuning the pitch of an instrument (via inst.macros feedback on pitch modulation) to an array of predefined harmonic steps of the base note, so you could zoom with a dial and repitch the sound to natural harmonic sequences. I used a table of harmonics which then defined a scale, and instead of playing a pitch, you’d play a base note and use a knob or pedal or modwheel to scan through that scale.
So I can imagine, using the tuning functions of the ktrk code you can tune the filter, and then instead of a key tracker, you can use another formula which will translate the cutoff knob/envelope/modulation into discrete steps within the desired scale, and which will relay an update until the preset time (i.e. 1/16, 1/8, triplets etc.) had passed.
Of course this will only work with actual DSP filter devices; you could also control the (polyphonic) instrument filter with way with a macro, but it will not work polyphonic, all note’s cutoffs must be set to the same value. So using the Analog/Digital filter DSP device and going monophonic is the better way to achieve this. There is no formula action inside the instrument modulation, only in the DSP, so that’s why.
I could try to help you with this, but I’m currently ultra stressed out with different other things, maybe I can find an hour or two for it on the weekend.