Actually, my plan for converting the coastline was to copy+paste some of the existing coastlines with the texture I want. That would necessarily alter the size and shape of the continent, and I think, why not?
After all, unless BT is some sort of bizarro parallel AT (They share borders, and even Cori is shared between the two), then the chances of two landmasses shaped exactly the same, with the same size, surrounded by ocean, in different geographic locations, would make the chances already near zero by geological perspective. From some more humanities perspective, the fact that the borders are exactly the same is not so much a problem, though still highly unlikely and contingent on the condition that the two continents are nearly identical physically.
That all aside, I just think if we are going to follow through with this idea, that we might as well make a nice change to BT's landscape to differentiate it from AT at a glance, not only from the now-old rumors about inhuman invaders.
