Dave, the ones I'm familiar with can be removed after you do a few things.
First, there is a safety pin that should be installed to protect against an unintentional discharge. It's like the safety pin that you remove from a handheld extinguisher, except this one should normally be removed so the automatic release can work. Hopefully the pin is dangling from a chain or cord. You also might find the pin neatly installed. This actually happen quite often, and disables your fire system. If it's installed, be thankful you haven't had a fire, and remember to remove it when you reinstall the bottle.
Second, with the safety pin installed, remove the remote cable release, if you have one. This is a cable release that leads to a manual release pull handle that will be located somewhere right outside the ER entrance. I don't know if these are required, so you may or may not have one. Don't attempt to disconnect it without first installing the safety pin. That's how you WILL accidentally discharge the bottle.
Third you can disconnect the plug for the pressure switch. It will not discharge the bottle. The pressure switch just indicates to the shut down system that the bottle is still full and it's OK for the machinery to run. When the bottle discharges, pressure is lost, the switch opens, and the engine(s) are shut down so they don't suck all the fire suppressant out of the ER.
Now you can remove the bottle.
Note that with the pressure sensor plug removed, your shutdown system should alarm, and you won't be able to start the engine, generator, or anything else that it controls. To silence and/or override the system to enable starting things, you press the appropriate buttons on the shutdown control panel. I think there is a silence button, and an override button.