Is there a setting to enable a quantization of part changes?
The only way I know is affecting Part 1 to pattern A1 and Part 2 to pattern A2, etc… and change patterns.
Not sure it’s applicable to what you want to achieve though because you might want to have long patterns and change several times the part meanwhile.
Quantized part change might be an idea to submit for next OS updates if it doesn’t exist yet. 
+1
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Did this ever get added? Started to mess with parts today and immediately seemed weird how clunky the timing was when switching parts with the sequencer running. I assumed it would switch to the new part at the end of the current pattern. From what I’ve read about parts it seemed like an obvious way to switch in some new default samples/variations etc when live jamming. But if it doesn’t switch on the start of the pattern it feels pretty hairy…
Either press it in time or make a copy of the pattern as someone else suggested.
Pressing it in time doesn’t always snap straight for some reason. Guess I’m misunderstanding how/why Parts are used.
Re-RTFM…
+1[/quote]
Did this ever get added? Started to mess with parts today and immediately seemed weird how clunky the timing was when switching parts with the sequencer running. I assumed it would switch to the new part at the end of the current pattern. From what I’ve read about parts it seemed like an obvious way to switch in some new default samples/variations etc when live jamming. But if it doesn’t switch on the start of the pattern it feels pretty hairy… [/quote]
Part switching are instant, as soon as you´ve pressed the button combo. Switching pattern (with another part) does await end of pattern. I don´t remember, be there might be an setting somewhere to overrule that default setting.
If you copy a pattern to another pattern location and then change/save another part to this new pattern, pattern switching will yield the result you are looking for.
you can jump to another pattern (and part) within a 2 steps interval.
Fo OP’s question, it has been answered. The only alternative for “quantized” part switch is by using the arranger.