Hi there,
Thanks for reaching out. I will try to help with your question.
Please note that we are limited in how much support we can provide for customizations such as this. That being said, I will try to help get you pointed in the right direction.
I dug into the code where the custom Attendee Information fields are to look into this. Unfortunately, there are not any action hooks or filters in this particular component that would allow you to do that without directly editing the plugin.
Many areas of our plugin are built with extensibility in mind, but this is not one of them.
I wish I had better news for you on this! Please let us know if you have any additional questions.
Thanks,
Sky