I would think the funktion of the <- -> keys should be to move quickly along the notes in a stave.
If it selects slurs and other objects, it interrupts the movement from note to note -
selecting things that are no noteheads and breaks should need a modifier key.
And I would prefere to have the up and down keys to change the pitch of a notehead.
Change the stave is imho a secondary task, should need a modifier key.
Please, could you rethink this concept? Using the ALT key every time
when I push a note up and down, often takes me out, to the menu, or I get
noteheads changed to breaks and so on. This does not work fluently.
Maybe, you could give us a option to determine what the left-right-up-down-keys
with / without ALT do?