funny enough you can do that in blender ~ open image texture in uv editor and then adjust the map to fit apply the textures and then bake back to original maps

you would have to bake back if you are using a merchant resource pack or you run the risk of the MR being extracted and thats against the rules ;-)

 

@EC would guess the verts you added are not on the material now so in edit mode select all (make sure you have the odd ones selected) then assign mat that should fix it