Can I forcibly turn the alarm output modules ON/OFF from a PC regardless of any input data alarms?

You can, starting with style 8 of the DA. Setting command: VS. Control execute command: VD.
The DR and DC do not support this. With DAQ32 and DAQ32Plus you can set up output relays, but you can't actually operate them with commands. You can also control relay operation using In Touch for DARWIN 2000.