Customize Magento Module (Plugin)

1:The current module has functionality to allow checkout with/without installments (based on order total). Would be preferable to also have a new logic that can add an extra charge based on selected amount of installments. 2:Also new functionality to cancel the order after a failed transaction is desired (canceling the invoice and restocking the products) instead of only leaving it as pending and showing a corresponding message to the customer. Original files and merchant integration guide can be provided on request. The ownership of the developed code will be 100% transferred to me and the code may not be shared to any other 3rd party. The new extension will not be offered through Magento Connect, it will be send to a client in a zipped format and installation should be as easy as possible. You can download the original extension, the merchant guide and the job description can be provided on request.