The Spring Lake 5 took a proactive approach to helping runners figure out how to get information on their registrations and make changes if appropriate. They sent out an email to participants to point them to a webpage on their own site with instructions, as well as the RunSignUp Widget to help them find their registration information as well as make changes.
Here is the email they sent out:
Here is the page after logging in and clicking on the registered race to change the T-Shirt size:
This type of integrated approach reduces errors as well as race director overhead in dealing with issues.