What do you do if your child's ultimate goal in life is sameness? What does THAT mean? He may only like a set number of foods, has few preferred activities and no interest in others. New is almost always viewed as non-preferred. Sound familiar?
The best way to help your child is to gently "push" him to do things outside of his comfort zone. This may be sitting at a new chair at dinner. He may need a visual support, social story or verbal preparation for a few meals before you ask him to actually sit somewhere different. He may balk at it when asked. Why? The anxiety of the situation causes him to revert back to his digging his heels in. The visual will help as will verbal prompting of the steps he already has practiced. Take this slow. Only tackle a few things at a time.
Using a first ....then strategy may be helpful. He must try the "new thing" before he can have or do a ultra-preferred thing or activity. It will take a lot of patience but it will open up an opportunity to expand your child's world. It is a step to helping him live and adapt to people who look at things much different than he does. Good Luck . Let me know how it goes.