I don't know, though you can pedal while shifting, as long as you don't present an appreciable load, as you note. I'm relearning how to ride a 3-speed now, and I'm often making the mistake of shifting down from 3rd to 2nd. On an old AW, this is a mistake, because I stumble upon the so-called neutral gear. It's unpleasant.

I guess you can shift the fixed hub while pedaling. I can't say how they worked that out. Maybe you can present a load. Or maybe not.