You really, really need to upgrade. 5.45c is over four years old, and many stability and security improvements have been made since then, not to mention features. Most of the things that you've hacked in (at first glance) are stock features now...
There have been a grand total of seven active topics in this forum in the past year. The 5-series is dead. It's REALLY time to move on.
Now, as to address your problem....
It's a tough one. The cookies are set using javascript in the 5-series, so setting the login cookie during a redirect isn't gonna be too easy.
My first thought is using another actual Javascript to redirect the profile edit confirmation screen to Ultimate.cgi... though they'd still see the confirmation page for a bit.
Oh, and if this really is their first login, you'll want them to redirect to Ultimate.cgi, without the BypassCookie bit. BypassCookie ensures that their new post indicators aren't updated...
