Need to trigger Custom ESS job rather than standard ESS job for sending Dunning Letters

In the Collections menu, under the customer profile, there is an option called "Strategies." Within this, there is a "Tasks" section with options like "Soft Reminder" and "Harsh Reminder." When selecting any task and clicking "Resend Letter," it triggers the standard ESS job "Send Dunning Letters." However, I need it to trigger a custom ESS job that will run and deliver the Dunning letters to the customer instead of the standard ESS job.