I have added a shower to what was just a tub in our older house. I really like the tile in the bathroom that goes half way up the wall. But with the shower now installed I need to expand the tile upward in the shower/tub. Like I said I like the tile that is already there. Can I just cut out the sheet rock where the tile currently ends, add backer board and then put my choice of coordinating tile up to the shower head? Also how do I deal with the window that is half way over the tub?