I don't know where you saw that someone could replace your cathode ray tube, but I doubt it would be possible. The CRT basically IS your monitor. The cabinet of the monitor needs to be designed to fit any particular CRT and replacing CRT's (unless it is the one that came with your monitor) I would think to be impossible.
However, a Sony CRT (these are in several barnds of monitors sold under the Trinitron name) gives all the benefits of an aperature grill type monitor. I am not going to explain as many discussions of the benefits vs problems of aperature grill monitors vs shadow mask tubes have been on these forums and the net.
So, replacing your CRT with something other than the original is not possible (or by any many means will be cheap). And, Sony/aperature grill tubes offer many advantages over traditional CRT's.