Ux is backwards for tablature editing
Regarding the up and down arrows changing pitches and the ctrl modifier being necessary to change strings:
The Ux should be defined in such a way that the default behavior without using a modifier is non-destructive to the note's value. It's all too easy with musescore to accidentally change the note value. It's a backwards Ux. Hitting the up and down arrow's default action should be to keep the note value and change the string. The modifier key should be required only when changing the pitch. That's pretty common-sense Ux.
This is what makes finale easier to edit tab than musescore. With finale I can quickly navigate through the tablature part of the document with one hand, changing strings assigned to tablature. With musescore, I have to keep my left hand poised on the control key the whole time.