function custom_allow_refund_op_login_format_payment_data($payment_data)
{
    if($payment_data['allow_refund']  && $payment_data['allow_refund'] == 'no')
    {
        $payment_data['allow_refund'] = 'offline';
    }
    return $payment_data;
}

add_filter('op_login_format_payment_data','custom_allow_refund_op_login_format_payment_data');