[otrs] Followup priority change

Hi All, Hoping someone can help me. I am wanting ticket priorities to change when a customer replies to an auto reply message send from OTRS. That is, when a customer first receives an auto reply after raising a new ticket and then replies to that ticket I want to the priority to change to a higher level. I have worked how to set ticket priorities when they are first raised but do not how to get them to automatically change after a followup. I have looked at the PostMaster filters and GenericAgent functions but they do not seem to offer a solution. Anyone have any ideas? Regards, Michael