It may be childish,but I really enjoy "knifing" the old air springs when I change them.hello mate you dont need to worry about your height sensors just changing the air bags will have absolutely no effect on them whatsoever .
as for the air already in the system you could try the way i did it by first lowering the suspension to the lowest setting then open the tailgate to stop the system trying to self level , you can then jack it up and start to change them , the small amount of air in the system is easily released when you disconnect the pipe i hope this helps.
rick.