Ok, I’m not completely sure on this, but I think the 2s over some of the bars just mean the beat has only 2 beats instead of 3. In one of my pieces I once played had a three over some notes covering 4 beats, but since the notes with the 2’s over them are already worth 2 beats, i think it means the bar just has 2 beats. I believe bars 210-212 is played normally intead of in a 2-3 polyrythym and the concept with the 2s is the same as I stated above. Attached is a picture of of how I think bars 210-212 should be played.
I think I figured out how to play it/count it though. I think what we're describing is called tuplets (duples, triplets, quadruplets in our case). The idea is that the 3/4 meter does not change. You fit the specified number of notes into the meter evenly.
I don't quite understand the illustrations you drew, but watching the video, the 2 in the bracket works similarly to if there is, for example, a 3 in a bracket (which indicates triplets). In this case, it means two quarter notes with the 2 over them fits into the space of 3 normal quarter note beats. So in reality their length is like a dotted quarter note each.
I don't think this is right since changing the number of beats to 2 in a measure would change the meter/signature. I don't think there's anything wrong with changing signatures in the middle of a piece but it's not typically done. Imagine having to adjust your metronome from 3/4 to 2/4 for 2 bars just to practice!I think I figured out how to play it/count it though. I think what we're describing is called tuplets (duples, triplets, quadruplets in our case). The idea is that the 3/4 meter does not change. You fit the specified number of notes into the meter evenly. Will post a picture on how to count them later.