O.L.
If you can avoid the changing table it at least won't be so dangerous. My DS1 used to always get changed on his changing pad on the floor. He loved to flip himself completely over, so I also got pretty good at changing him belly-down. My DS2 does the same, but I've been winning the battle so far. ;)
The high chair is tougher. I guess I'd just try to keep him occupied (hand him a spoon, a piece of food, something) so that he doesn't get upset. And if he does, redirection... or else take him right out of the chair and put him on the floor, so he gets the message that he can't do that in the highchair. It's still a bit early for real discipline, of course, but he'll get the message.
Best of luck!