The Mission: Impossible franchise took on its toughest challenge when it made the decision to film two M:I movies back-to-back. The decision was only made more difficult by the global pandemic that first delayed Mission: Impossible 7 entirely and then caused shooting to run at a snail's pace once it could begin again. This caused a lot of new and unexpected complexities in production, including the fact that Tom Cruise needed a wig for some scenes.
We already know that the Mission: Impossible - Dead Reckoning reshoots were a little wild, with some shots taking place at Tom Cruise’s garage because director Christopher McQuarrie realized he needed some new shots at the last minute. But speaking with the Empire Spoiler Special Movie Podcast (via ScreenRant), he also reveals that reshoots required Tom Cruise to be in a wig for a few scenes, including the final moments between Tom Cruise’s Ethan Hunt and Haley Atwell’s Grace. McQuarrie explained…
Apparently the first of the two Mission: Impossible movies being filmed evolved enough over time that by the end the original version of the farewell scene wasn’t right, so it needed to be redone. The problem was, Tom Cruise had very different hair by that point.
The issue was the reshoots for Dead Reckoning Part One were taking place while principal photography for Dead Reckoning Part Two was happening, and apparently Cruise has very different hair in that movie, so it needed to be covered in order to work in the earlier scene. McQuarrie continued…
Tom Cruise has gone back and forth between his Top Gun-style short hair and a shaggier style throughout his career, and even within the Mission: Impossible franchise. It sounds like he may be doing that even within the two parts of Dead Reckoning.
This is actually a potentially interesting detail as it would seem to confirm that Part Two isn’t going to pick up immediately after the events of Part One, or at least there will be a significant time jump at some point in the film. How else will Cruise's hair be changing so much? It makes a certain amount of logical sense. When you’re busy saving the world, who has time to get a haircut?