Yes, in fact all commercial airliners have both an automatic mode and a manual back up for cabin pressure control. Most of the newer Boeings actually have 2 automatic controllers and manual back up (757-767-777-747's)

If a person knows hot to operate the system in manual, it's an easy thing to open both outflow valves and turn off the pressurization system, and let the cabin altitude climb up to cruising altitude. Now, you would NEVER do this, unless you had smoke/fire and you were below 10,000'.

Yes, in some Hollywood movie, staring Bruce Willis, I'm sure the pilots did just that, and the pilots put on their O2 masks, and all the people in the back, including the would be hijackers, passed out from lack of oxygen. But they would wake up when you descended to below 14,000' or so.

I guess you could take the plane up to 45,000' and depressurize it, stay up there until you think everyone in the back is dead, and then come back down, but you've only got 1hr. of O2 for yourself, less if you are at 45,000'.

It happens all the time...in Hollywood. (insert large eye roll emoticon)