Is there an addon which rebinds camerazoom (mousewheel)to another action/spell while in combat and rebinds back to camerazoom when put of combat? . I would like to cast Mana shield with mousewheel in combat, and zoom in/out when out of combat
No such addon I know does this, but it is possible to write one. Not very advisable to rebind zoom to mana shield though, you could be placed in combat during a very inconvenient moment and unable to change zoom easily.
I don't think you can change keybindings while in combat...
Anyway, SmartBuff doesn't change the binding. It unbinds zoom in/out and changes the mousewheel binding to SmartBuff. Then, in the code itself, SmartBuff controls your camera zoom in/out. If you want proof, disable SmartBuff and try using your mousewheel to zoom. It won't.
AddOns may not change bindings while in combat. However, what he's asking for is changing the binding just before entering combat and then changing it back just after exiting combat, which is definitely doable.