Ok, so a quick update - the clonazepam ran out about 2 weeks ago (now about 8 months post op), before that I had to take half a pill and then quarter of a pill for a week each because I could not take the withdrawal when I tried to stop completely (I was careful and tried that stunt before all the pills were gone).
I had quite a few side effects from stopping the pills - opposed to having no side effects while I was on them at all. But when I stopped, I had some dizzyness, nervousness, increased tendency for muscle cramps, belly cramps. My throat felt rougher, dry and I have a foreign body sensation in it at times.
Pitch dropped by about 2 semitones, so my relaxed voice now averages at 160 Hz (but its not hard to use a little bit of effort and control and get to 180 or even 200 Hz). I sent in my voice files to Dr Kim and he basically suggests I should take more clonazepam - or one of the two alternatives he suggests. He does not recommend Botox though, even though I would be more comfortable with that rather than those pills. But he writes that my pitch has stabilized, so I should not do Botox.
I am not sure what he means with that - my pitch has stabilized at 160 Hz?

I am not quite happy with taking more pills though - I did not have the impression that they helped THAT much and in the end I will have to live without those pills - I can't take them forever... so I am really unsure if I should follow Dr Kims advice now - in addition to that, no doctor I know of would prescribe me an antiepileptic psychopharmaceutical drug for pitch instability in the voice - up to now most said that their recommendations would be voice therapy instead. One even said I should do psychotherapy because the psyche has such a big influence on the voice.
So my tendency is that I probably have to deal with the remaining issues with conventional voice rehab. The remaining issues (if I take it that the base pitch now has stabilized as he said) are pitch instability (I can not hold one pitch and maintain it for some seconds), voice break (strong pitch instability at around the C4 note, around 250 Hz), some remaining hoarseness or breathiness and some tension, which mainly comes when I try to speak in a bit elevated voice to be in the ~200 Hz range instead of 160 Hz for a longer time.
Does anyone have suggestions?