Magento/Paypal Payment Failed message Customization

ATTENTION!: This project is for AMERICAN programmers, working out of the USA Only! I am using Magento Community Version 1.5.1.0, and use Paypal API for all site transactions (paypal express & paypal payments pro). When there is a failed payment transaction, paypal provides the customer a message like: "PayPal gateway has rejected request. This transaction cannot be processed (#10505: Gateway Decline). " These type of codes and messages are not clear to the customer as to why the transaction was declined, and I would like to have Magento produce a custom written message for specific errors, I have about 4 or 5 error code message to customize. For example: Original Message: PayPal gateway has rejected request. This transaction cannot be processed (#10505: Gateway Decline). Custom Message: Your request could not be processed due to the billing address mismatch. Please ensure the billing address entered matches the one on file with your credit/debit card. Call us if you need further assistance. Thank you. Thank you.