Do you mean saving it permanently between sessions, or just inside the game?
The zoom function does "save," I think, just by use. When you toggle zoom on, it will zoom to the degree it sat when last used. Naturally, this mostly happens when you were last in a gv at max zoom for shooting -- and now you want a slightly closer look through your plane gunsight, but you end up seeing just the center dot of your reflector....
As I understand it, zoom is more of a GAME setting and not an individual AIRCRAFT setting. So, I dont beleive you can save it the way you do head positions, with different settings for different planes or gun postions. Zoom applies to views, and to the clipboard map, all with the same degree.
I have my increase/decrease zoom mapped to a pair of joystick buttons, and it works really well for me.