In order to prevent abuse of our registration system, we do have some limitations in place. There are a number of existing integrations you can use that will import customer registration information from other systems: https://support.logmeininc.com/gotowebinar/help/add-gotowebinar-registrants-to-mailchimp-g2w160007
I apologize, as a rule we don't generally support integration inquiries here, because we have a developer support form available here: https://goto-developer.logmeininc.com/api-support-request-template
In general, we don't condone customizing registration links outside of their intended use. If I do find any internal documentation referencing your request, I will certainly update this post.
What about a custom field that someone has built such as a "who referred you" field? Is there a way to customize the url link so that it automatically fills in my information?
@mschellinger What you can utilize is GoToWebinar's Source Tracking functionality in order to see where each registrant is stemming from: https://support.logmeininc.com/gotowebinar/help/source-tracking-beta-g2w090114
A vendor is setting this webinar up so I have no control over the back end set up. I can either ask people to put my code in and hope and pray they do it or make the URL prefill. If there is a way to prefill a custom question please let me know otherwise my only option is hope and pray.