I started my Toyota Corolla ATF changes at 83K and am at 153K with zero problems. If you're worried, change out small amounts at first to ease into it. Not really necessary, but it makes some people feel better.
Thanks to everyone for their thoughtful ideas. Car now has 126k and am going to start a new thread on new situation. Again, thanks for all the responses. I avoided flushing but may not be any better off as a result.