Hello, I want to record my Yamaha Reface YC on a mixer/recorder. I usually do it on a stereo track, but this time I'm going to need to record it on 2 separate mono tracks. I use the rotary effect on the YC so, as long as I adjust the mono channels identically, will there be any difference in sound compared to recording on a stereo track? I guess I'd have to pan one channel to the left and the other one to the right, correct?

Correct - if you fail to pan one channel hard left and the other channel hard right - 2 MONO tracks = 1 MONO track +3dB.

It will only make the sound slightly louder, if both MONO tracks are panned to the Center. In order to recreate the stereo illusion, you must pan one of the mono tracks left and the other right. Even though FM is famously mono, the Rotary Speaker effect is famously stereo. To get the movement you need to pan the tracks to opposite sides.

Recommend: play with the pan positions after you record - you should be able to hear a very distinct difference when panned out in stereo versus stacked in the center.

Hello Bad Mister, thank you very much for your answer. I've managed to do some trial today and you're right, the sound it's completely different when it's panned to the middle versus to the sides. I have to find the exact degree of panning that suits me best, but just playing with it I got very different results. However, I've compared the sound of the dual mono and various degrees of panning versus the keyboard recorded in stereo, both options with speaker rotation and level matched, and they don't seem to sound exactly the same to me, but I don't know if it's just my impression. Does this make sense?

They will only sound exactly the same when one is panned hard left and the other is panned hard right. All other settings for panning will be different from recording in stereo.
It's like a four sided rectangle is only really a square when all sides are equal. The stereo illusion is made up of a left channel with only left channel information while a right channel should have just right channel information.

Hello Bad Mister, ok. Thank you very much for the explanation

Only 1 more question: as in any music recorded without rotation effect the stereo is more static, and with the rotation effect there's a movement from one side to another passing through the middle, would this side to side movement sound the same when recorded on 2 mono tracks and panned to the extremes respect recording it on a standard stereo track?