In my opinion, hacking the registry is not an valid option.
I've been working with exchange now for a few years. And the last think I would want anyone doing is hacking up an exchange servers registry.
If you can't configure the product thru the front end, (we are talking about windows, not linux) then it is not worth it.
Trend and Mcaffee's groupshield allow you to block extenstions. Which is the preferred scenario in anti-virus protection. You should *NEVER* rely on virus definitions. They are only as good as the last update. Ans someone has to be infected first in order to create the update.
I am not willing to take that chance on any network that I work on. I do not even rely on Mcaffees virus definitions.
As far as intusiveness, I get this all of the time. Maybe norton has gotten better, but I doubt it. If I had a penny for every time I fixed a machine by just removing norton and manually cleaning the registry, I would be a rich man. This can not be disputed, Norton has a long history of "adding features" to "help" the os when in fact it hurt's the os. Just like AOL writing their own tcp/ip stack.
Mcaffee does have a web based interface for their new line that allows central administration of users desktops.
As far as exchnage goes, trend and mcafee both plug-in to exchange, which allows you to administer the AV product from within the Exchange Admin program itself.
The moral.... never trusts AV products to do the work for you. It's bad administration.