When adding an existing user to a blog (in the admin panel), a very basic email is sent. I am trying to overide this email so it is a bit more attractive – to at least have a clickable link.

Looking in user-new.php, it doesn’t appear to have an apply_filter.

How can I change this email without an apply_filter

The email is

You've been invited to join '%1$s' at. 
%2$s with the role of %3$s.

Please click the following link to confirm the invite:
%4$s'