Lower weight rated wd hitch on a heavier trailer, unsafe?

The blue ox wd hitch Im looking at has the same hitch/head on all models, bars will interchange.
If you go to a heavier trailer all you have to do is upgrade bars.
What could be the results if you dont upgrade to heavier bars if going to a larger trailer?

Depends on the tow vehicle. If you are towing with a one ton dually you might not want any weight distribution depending on the tongue weight. Why would anybody want to redistribute weight to the front axle on a heavy diesel engine one ton that has a payload of 6000 or so pounds and almost all that payload weight is designed by the manufacturer to be over the rear axle? Just get a sway mitigation/control feature and make sure the receiver is up to the tongue weight.

It all depends. Some trucks (long wheelbase diesels) don't need to put much weight back to the front axle. Other trucks weight distribution is more important. Smaller bars simply won't distribute weight as well.

If it is safe, why doesn't Blue Ox just only sell the lower rated bars?

The bars are basically useless. In order to transfer enough weight to work properly you'll bend the bars; rendering them inoperable anyways.

What icanon stated. Plus just guessing, if the bars were grossly under rated, they may bend out of shape or not control a sway situation as well. :@

Oh well, I see dodge guy posted his reply while I was typing.

You very well may bend the bars! my neighbor has a Blue Ox an has a bent bar, looking at the bars they look like they can be bent very easily!

Good question. I believe and maybe wrong but having a lower rated wd you cause you not being able to shift all the weight, prabably some but not all. In other words lets say you need to shift weight of 200lbs but the lower rated wd would only shift 125lbs. This maybe acceptable, again I maybe wrong, providing you only needed to shift that 125lbs or less.