Cargo on Passenger seats

Hello Ladies and Gentleman from Dubai: I have 2 questions regarding the possibility to carry cargo in the passenger cabin, on passenger seats IAW 25-855 Amendment 26. The first one is related to the cargo of mail restriction. In my experience, mail have been carried by European operators as cargo on seats for many years; Is this a new rule? what is the reasoning? Second question has to do with the oxygen generators in Airbus family. CS25 states: "...For centralized passenger gaseous oxygen system, the applicant should get confirmation from the aircraft manufacturer that no oxygen is present in the passenger oxygen lines under normal operation. If confirmed, the opening of the PSU oxygen door should be forbidden by using for example the test knob button....For decentralized oxygen systems, gaseous or chemical, the applicant should either remove the passenger oxygen system, or assess the maximum temperature to which the PSUs could be subject in case of fire developing in the cabin..." Airbus uses Decentralize PSU units on top of seats. Will you agree those units must be uninstall before operations or, since no oxygen is in the lines, deactivation of the units is enough? Thank you