Those shortcuts you gave only work in the following circustances:
- If you’re writing a higher note then the previous, ctrl + alt will write it an octave lower
- If you’re writing a lower note then the previous, shift + alt will write it an octave higher
Otherwise, those modifiers have no effect.
So, for example, if you write a C, then write a B, it doesn’t matter if you press just B, or ctrl + alt + B, it will (in both cases) write a B a semitone lower then the C.
And if you write a C, then write a D, it doesn’t matter if you press just D, or shift + alt + D, it will (in both cases) write a D a semitone higher then the C.
Is it not possible to have modifiers that will always write a note in a certain register, regardless of what the previous note was?