Does the new Rockbox fw support changing tracks with the screen off?
By default, all buttons work with the screen off (but the first button you press turns the screen on at the same time as performing the function).
There's a hold button (the power/sleep button) which locks all buttons until the power/sleep button is pressed again.
There's also a setting for first button press turns screen on (which I use) which makes it so that any button you press turns the screen on only, and then you have to press the button again for the function. I do this to prevent accidental track skips while the player is in my pocket.