carrying weight on rear bumper to offset tounge weight.

Apart from the possible structural consequences --
reducing TW by adding load to the far rear of a trailer, IMO, is a bad idea.

Adding load at that distance from the trailer's center gravity has a big effect on the trailer's polar moment of inertial.
Both the decreased TW and the increased polar moment of inertia tend to decrease the trailer's yaw stability and make sway more likely.

If you need to reduce TW it is much better to move load from the front of the trailer toward the center of the trailer.

Ron