Can I add a Cancel/Modify button to my form to cancell payments using integration

Can I add a cancel/modify button to my form to allow recurring donation's to be cancelled or modified without having to contact Dwolla?

Unfortunately you cannot do this payment process directly within the form. You can only do it within the payment gateway dashboard (in this case Dwolla)

The form submissions with regards to payment integration goes only one way. Meaning it will only submit the transaction to the payment gateway, and then the payment processor will be the one that will process actual payments (credit or cancelled)