Heavy duty vehicle (HDV) platooning has been widely accepted as a solution to reduce fuel consumption and traffic congestion. However, the control strategy for HDV platoons interacting with other vehicles is not yet well established. This work presents a new framework for handling the requests of passenger vehicles (PV) plugging in or out of an HDV platoon. It consists of three main steps. First, the basic cruising control of the platoon is achieved by a distributed model predictive control (DMPC) scheme. Second, redesign of controllers ensures the stability of closed loop Plug and Play (P&P) operation. Finally, a transition phase to steady-states guarantees the feasibility of the newly synthesized controllers. Additionally for the plug-in case, we propose a novel approach of Formation Coordinator that determines the optimal location at which the redesigned controller has the best initial feasibility. The performance of the proposed control framework is illustrated on a multi-vehicle platooning system.