First, congrats on being so careful about virus, etc; this can be a cruel world. That being said, there is no need for your extra layer of caution. I understand what you want to do, but there are so many security features built into 7, it is not necessary.
In lieu, of your precautions, which are causing you problems, may I suggest a program, that will inform you every time a change is made; authorized or not. Win Patrol, I use it and it will notify of every change and give you time to refuse the change.
Win Patrol. http://www.winpatrol.com/
I use it and it is great. It will give you that extra feeling of security that you seem to want. Incidentally, I want it too.