Oh I see... Is it something you can only do with the Gamecube controller? Because I can't seem to do it with the wii remote on its side which is how I usually play brawl (Don't judge me, I like NES style)
Nevermind, I just tested, and you can't even move the camera around when you focus on the characters. Just rotate it, at most.
You can set the camera as fixed in special mode and the replay will keep that. However, it won't zoom on a specific part.
EDIT: I think I remember a code which kept the camera in the position you set when when you unpaused the game. But I have no clue where you can find this code.