I need to duplicate the check payment method and I've followed this guidelines: http://www.magentocommerce.com/wiki/duplicating_money_order_payment_method_module
Everything works as expected but I had to modify core files as the guide stated and I want the website to be able to be updated without breaking this.
I had to edit for this the app/core/Mage/Payment files that follow:
and added copies of the checkmo.php files where they were needed.
I tried to replicate these changes inside app/code/local/Mage/Payment but with the same code I can't see the payment method now. I'm guessing this is not the right way to do this. How can it be done?