For Owen you just try to deal with the tantrum (which is not pleasant got anyone) or avoid avoid avoid!!! When we were at disney in June there was a day that almost all the rides in MK were down at some point in the day. Thankfully since it was raining buckets the lightening and thunder was distracting him.
In his case we would change/plan it trip dates around a barnstormer refurb. No question there. If barnstormer was down unexpectedly we would accept the initial tantrum then not go anywhere near storybook land
/go to another park.
And again these are not "typical 4yr old tantrums" but we are so much better at handling them and he is getting much better at dealing with change.
But that is just us.....