When loaded outside the kern, you just have a triangular pressure distribution on part of the footing. It is usual practice to restrict the maximum pressure to the same value as for uniform pressure. I am unaware of any procedure to calculate the rotation, and if there were, you would have to take it with a grain of salt...after all, this is soils engineering. I always try to use better solutions, deeper and less wide, or with rectifying perpendicular beams.