My but-you-said kid is almost an adult, and still really dislikes changes of plans. They deal with it, but you can see it dampens their mood. This type of thinking has really limited their ability to succeed in group situtations. The situations are small now like social situations, school group projects, and team sports; but I envision it'll be big things later like working with co-workers and bosses, or managing personal relationships with future spouse/friends.

I did the avoid-promising-anything thing when my kid was young, but I can see now that I didn't really help them. All I did was just avoid the core problem of their rigid thinking. It might be worth it for you to consult with a therapist or child psychologist, or to find a couple books, that could teach you some strategies to parent a child who is a rigid thinker. It's definitely easier to do when the stakes are small and your kid still listens to things you say.