Per the 2015 Ford F-150 Workshop manual: “NOTE: The rocker panel inner reinforcement on the SuperCrew Cab is a two-piece component consisting of a front and rear sections. The front portion is an extrusion casting and may not be sectioned. The rear portion only may be sectioned. The following procedure assumes full component replacement. For rear component sectioning Refer to the instruction sheet included with the component or on the PTS (Professional Technician Society) under the Service Tips tab for this vehicle.”

The procedures can be found at www.motorcraftservice.com

Here is a short video that shows how to access the Ford collision repair information.