A revival may not have significant changes, but some new works have substantial changes between first preview and the critics' performances. If something is not working, the creative team tries to fix it. Material can be cut or added, scene order can be rearranged, and sometimes those changes can be quite significant. If I remember correctly, both Reasons to Be Pretty (on Bway) and Prayer for My Enemy (off-Bway) completely changed their ending between first preview and opening night. On the other hand, A Behanding in Spokane, even though it was a world premiere, had no substantial differences between 1st preview and opening, as far as I could tell. It is a little unpredictable.
A revival, or a production that is a transfer from somewhere else is less likely to have such drastic changes, but still could (as in some recent changes in key cast members during previews).
"What was the name of that cheese that I like?"
"you can't run away forever...but there's nothing wrong with getting a good head start"
"well I hope and I pray, that maybe someday, you'll walk in the room with my heart"
