Which hook to use?

I don’t know. Maybe you can customize the template for it? https://www.s2member.com/kb/pro-forms/#customizing-pro-forms

In the custom field editor, you may find these settings useful: Allow Profile Edits, and Other Attributes.

I hope that helps. ??

Ended up not needing an s2 hook. Used a general wp hook:

add_action( ‘register_form’, ‘myfunction’ );

function myfunction() {

my stuff

}

Cool ??