I doubt if Keystone will give you the go ahead, due to them owning the responsibility, if a problem arises from your walking on the roof.
I asked the tech, that was prepping my new FW, if it was okay to walk on the roof. He said yes, it holds my 220#s just fine. I mentioned that I'd just looked at the owners manual, and it said do not walk on roof. Then he said it is not recommended, but I know where to place my feet.
To be fair, my manual is covering many different models, not just mine.
I have noticed some brochures do say, full walk on roof.
Jerry