I seriously doubt there are many systems in a aircraft that can’t be disabled. The oxygen system is definitely a system that would have a off switch. You wouldn’t want it deploying if there was a fire in the cabin. It would be like pouring gasoline on a match, even with the relatively low flow of the masks included on planes.
Would you like for me to explain the oxygen system for the passenger or would it be easier for you to look it up?
Hint, there are NO oxygen bottles and for that matter NO oxygen carried on board the airplane for the passengers.. Depending on type of aircraft One or Two bottles for cockpit crew. There are portable oxygen bottles on board. 777 may have a dozen. Not sure the exact amount. Can be used between 15 and 30 minutes each depending upon the flow you select
Wow, I bet that blows your mind.
Hint. They are call oxygen GENERATORS. Ya cant turn them off. I dont want to have to explain. Just got to google type in "oxygen generator" + airplane. Am sure you can read all about it