Disabling 'register' for a while

[Jawelin]

Hi. In the option settings is written:

Allow new user registrations
If you would like to temporarily (or permanently) prevent anyone new from registering, you can do so. The REGISTER button will still be seen throughout the BB, but anyone attempting to register will be told that you are not accepting new registrations at this time.

Well. I would disable for 'mantainance' reasons new users for a while. So I would:
1) Remove the register button into board (guests aren't allowed, as long double registration per user) so I should check every time those settings and hide the button on top bar

2) Most importantDon't display the 'Register' link on first page when they aren't allowed, optionally adding a new <list> item explaining this is for maintenance reasons.

How should I modify what template ?
Could I make some 'if' choose whitin it ?

Thanks a lot.
Bye