Can a medpor jaw implant be added to the top of an existing implant or will I need to remove the existing implant?

Hello I have jawline Medpor implants. I'd like to know if it's possible to add an implant on top if I want a longer jawline (change of design)? Or do I have to remove the implant? I've had them for 5 years, so they're already fixed. I don't want any filler or fat