Being able to shift the texture is unfortunately not possible yet... but it sounds like an interesting feature (in combination with local texture alignment). I will put that on our to-do list
Although for this feature it's necessary that the block preview shows the texture... this wasn't implemented yet because it's a bit tricky to show the correct alignment on the block preview...
We'll also have to think about a proper way to control that... maybe adding another key for it? E.g. hold the key, then use the arrow keys to move the texture?
I am thinking similar to existing block resizing with arrow and page keys, though at some point you need to think about all the modifier keys. Could use control under shift but that is crouch.
It could use the grid stepping for the amount of shift. For example I use a castle wall texture that has a grid to represent stack blocks, it aligns with the half block grid with the texture resizing I use. So I would want to move the texture just like global texture mapping would do for straight stairs, but for curved stairs I need to use local remapping and do it manually.
creative mode change texture already previews the texture, so instead of this being a preplace change just make it an edit change and leverage that preview though the red texture shade is unwanted and it should do a better selection of which texture is being edited like a ghost outline on the block.
Controller support is going to require more accessible controls - the game is currently not playable without mouse/key the controller support is not adequate - and adding more key modifers is not going to help. The popup menu circles are a good start for controller support but it does not support them yet. But instead of a key modifier maybe a modal select for the arrow/pg keys to be rotate/size/texture. Also many games use the left/right upper back paddles as modal selects - very intuitive to use but harder to learn.
Maybe just make shift a mode toggle rather than a hold mode.