Custom Field to registrant detail page

Hello,

need custom fields on my registrant detail page (joomla backend) for cancelation. Should be a text input field where I can manually enter cancelation fee (in percent).
Is there a built in solution for this use case or necessary to solve this with an override?

Best regards 

How about creating a custom field with Access level set to Special (so that it won't be displayed on registration form) but still being displayed when you edit the registration record (backend) ? Then you can enter the information you want there

Tuan