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Done

I would suggestion you to read a bit about scales and intervals to understand how music notation works. A# and B♭ sound the same and indeed overlap on the same pitch but in the context of intervals they have different meaning, and ppl that studied music knows this well and expects to see the correct note in the MIDI editor.
Did you ever asked yourself why they even exist?
Take for example the Cmajor scale → C D E F G A B do you see the intervals (2-2-1-2-2-2-1 semitones)
now let’s consider Fmajor, standing to what you say we can write it → F G A A# C D E F but do you see the problem?
There is A followed by an A#, but the 4th interval of an F is some kind of “B” note not an “A” note. Moreover writing it on the pentagram would be a bit problematic cause you need to write A♮ to cancel the effect of the A#.
For this reason you write that as B♭ and being a musician you want to see B♭ as 4th note of the scale and not an A#.