I don't do well with changes of plans either. For years I would get all bent out of shape, cranky and very unpleasant when my husband would call with a last minute change (even something simple, like going to dinner at someones house). I finally sat him down and explained that I just flat don't do well with last minute changes as it brings on serious anxiety, my brain needs time to process the change of plans (like a couple hours or more).
This has worked amazingly well. Now instead of telling me when I get home that we have been invited to dinner, he will call me at work, inform me of the invite and I tell him that I'll let him know in about an hour whether to accept or not. I know myself well enough now, that I can usually say, "it will probably be yes, but I just need some time to process".