config mode: info for visitors / admin only access

Hello,
ATM, when I update the installation, I switch to configuration mode because I don't want to have users using the gallery while I update.

I think it might be nice if the users would then see a message that explains to them that the installation is currently being updated. I guess I could add this somewhere in the language files, but maybe this could be done by default. I.e. sth like:
"If you are the administrator of this gallery setup, make sure to turn off config mode [= current text]...".
If you want to visit the gallery as a user, the gallery is currently disabled for maintenance blah blah [...] Please try again later. Admin email address: [....@....com]."

Also, I am wondering if it would be possible to have some sort of admin-only access, i.e. normal users would only see the login link + a message that gallery is currently being updated. If an admin logs in, he would see the gallery in normal mode (not in config mode). This would be useful after major updates, in order to test the key features before letting users in.

Thanks.