P24D1 seems to be a relatively uncommon code, related the the differential pressure sensor (or lines leading up to it) monitoring when to trigger a regeneration. I have my suspicions about what is involved in reprogramming the PCM, and don't think it would involve wrenching on the car. If, for some reason, the technician was underneath the vehicle and was trying to reposition the exhaust system, the differential pressure sensors lines are typically quite delicate and rusted to the exhaust system. As a result, they break pretty easily if you try to disconnect them. Ask me how I know.
Is it harmful? Based on the % full you are reporting, it seems to me that the DPF may never be indicating that it is full. Worst case is that it completely plugs up. The other scenario is that the DPF constantly reads full and the DPF is in perpetual regeneration. This is harmful in that it would dilute your engine oil with diesel fuel over time.
As an aside, you imply that a DPF would be covered under the Ford ESP plan. I bought as used truck that came with the Ford ESP. My reading of the plan is that under no circumstances is a DPF replacement warranted, as it is considered a "wear item". If a faulty sensor reading plugged the filter, I think you'd have an argument
