Save old emails?

[Boofo]

I want to update a hack that I used on vb3.0 that would save the old email address if a user other than usergroup 3 (awaiting email confirmation) changed it. The old hck used 2 queries in the profile, 1 to pull the email and one to update he profile field. I used a profile field to show the old emails but to admins only in the profile.

I'm not sure where to add it (the hook location) now and can I do it without 2 queries?