Fair enough. I think talking to RT is a fine idea. They may well provide useful information. However, if by "getting their permission", you mean get them to agree to include the consequences of your modifications under their warranty, I predict that your odds of success are approximately nil. Why would they possibly agree to such a thing? Your changes are completely out of their control. And, if you don't expect them to say that, what DO you want them to say?
My only point was that the warranty is simply not a factor one way or the other. On the one hand, they will never agree to warrant YOUR changes. On the other hand, the law does not permit them to penalize you for making such changes. You are on your own: if you break it, you own it; If it breaks in a way that you didn't cause, your warranty will be fine. All manufacturers who sell in the US understand these rules of the road and they will almost always respect the law. It is very unlikely that you will find anything to the contrary "in writing somewhere", and if you do it will be meaningless.
