我不完全确定定制表单是否有这样的操作挂钩（其他人可能知道），但如果表单正常提交，没有ajax，肯定还有其他方式。

如果你有任何问题，请告诉我。

//This applies if you want it to happen only if form is submited and page refreshed
//It doesn\'t work if user comes back later - there\'s no extra field later on

$form_submitted = false;

//If submit is pressed
if( isset( $_POST[\'submit\'] ) ) {

    //There should also be a nonce check here

    $form_submitted = true;      
}

//All your form html here

//Check if form is submitted
if ( $form_submitted ) {

     //Show your extra fields
}



/*If you want it to be a bit more "permanent"

1. update_usermeta() to save the bool that user has submitted the form - logged-in users only
2. Use cookies which might not work properly in browser "stealth mode" and is gone if user deletes browser history with cookies 
3. Use sessions which destroys itselves if user closes the browser

*/