You can swap out the hitch very easily. I swapped my 5K lbs one out for a 16K lbs one. The hitch cost $250 on Amazon. Was very easy to mount the new one. I also tow a Jeep, which weighs about 5K lbs and my trialer is around 1.5K lbs.
I spent a lot of time working on this issue, and you will be fine doing what you are proposing. In my case, spoke to chassis manufacture, Ford, who explained to me that their chassis was rated to pull X (can't remember the exact amount, was like 12K or 15K lbs.)
Then spoke with the coach manufacture, who told me that they put a 5K lbs hitch on for to prevent seveer overloading. The coach manufacture did agree that the chassis was rated for what Ford designed it for, but they choose to install a smaller hitch for the idiot factor. Their thinking was, if we put a 10K lbs hitch on, people would try to hook up a lot more than 10K. So we put a 5K and knowing that people probably wont exceed 10K.
In my case, my load is around 6,500 lbs. I swapped out the hitch to the biggest one I could find.
This is kind of the wrong place to look for answers to your question. Their are a lot of people who tell you the sky will fall, your coach will explode, and you will put their familys life in danger by changing out your hitch, trust me on this, I made the same mistake you did when I asked the same question.
IF you go to any of the racing forums, off-roading forums, etc., you will find hundreds of people who will gladly help you through this. If you ever go to any races, off-roading places, or big weekend events, you will see thousands of MH all towing everything imaginable, and none of their rigs are RATED to tow what they are pulling. Evey single time I go to an event, I ask everyone I can, if they have ever had a problem, the answer is alway NO. Also ask if they have ever heard of anyoen having a problem, the answer is also NO.
Good luck!

