rpress_insert_user_data

This filter is applied to use insert the user data, it is including two parameters.
$user_data -> is a string containing user data
$user_args -> is an array containing arguments of user data.

An example of how you can append is below:

function add_user_data( $user_data,$user_args ) {
$user_args = array();//containing user data.
return $user_args;
}
add_filter('rpress_insert_user_data', 'add_user_data', 10, 2);