The thing is here that the rocker switch already in the cab is a standard always on/always off type switch rather than a NO/NC type like a power button. It's not that I want to replace the power button with a rocker-type NO/NC switch but that I want to use the always on/always off type that's currently controlling the monitor on/off to put the PC in or out of standby state. Is this doable?
Perhaps I'm not fully caffeinated yet, so forgive me if I'm not understanding 100% what you want to do.
But...
If you use a momentary switch to power down your PC, your monitor (I am assuming this is a normal PC monitor) will also shut itself down when the signal is gone. OK, technically it's not a full power off, but it goes into a very low power state, usually on the order of only a few watts.
If you want a total power off, or you are using an aracade CRT. then get yourself a
Smartstrip. The PC is plugged into the smartstrip trigger outlet. When the PC powers off, it completely shuts off everything else plugged into the the switched portions of the strip.