X5Paul

Hi guys/gals, Im new to the forum and I currently run a 2013 520d, I am considering a 7 seat X5 on a 2007-2009 around the £15k mark if I can find one, but the 7 seat option seams to be few and far between, does anyone know if the two extra seats can be added at a later date? This would allow me to buy a standard 5 seat version and have the extra two added, thanks for your help. Paul.