What are Accordion Registers? Do You Need Them? 

i love the sound that the accordion makes when the simultaneous reeds are slightly detuned. its like a chorus effect. it's funny because in my band class at school we have to tune to completely eliminate that wobbly sound, but on the accordion its almost like a vibrato!

You couldn’t retune the one without the registers to octave tuning, you would need another set of reed blocks as the lower octave reeds are a bigger size to get the lower pitch. You could however change the detune between the reeds to get a wider, or lesser chorus effect when both reeds sound in unison.

You might be able to play the thing, but it appears that you've got absolutely no idea how they work.