You should be able to add a registration confirmation email using Universal Email on the registration page. You'd want to make sure the redirect setting isn't set in the Insert Record server behavior so that it only redirects after sending the email.
See if there is already a universal email server behavior applied on the registration page, and if not add one and update the insert so that it doesn't go to another page before the email is sent.
You could add universal email to the admin section with a button to resend the welcome email, or anywhere else... I guess that depends on when you want the welcome email resent. Either way it would be done by using universal email's server behavior.