Normally this wouldnt be a problem as the uv co-ords are on a 0-1 scale and changing the texture size has no effect on this as long as you use the same width/height ratio as the original, however the .mesh files use two textures which are treated as one for uv purposes so you'd have to increase the size of the attachment set texture as well. Its pretty pointless doing this though as the engine will just use the mipmap closest in size to whats been displayed on screen so unless you're running at an insane resolution and zoomed in really close you're just wasting texture memory.