I'm afraid you can't currently specify the post on the command line. I have added this to the to-do list. The currently available command line parameters are:
SheetCam TNG /p /s /l <job file name>
/p Run the post processor and exit (you need to also specify a job file)
/s Do not show splash screen
/l<license file> Install license
As a workaround you can go into program files and make a copy of SheetCam TNG.exe. Call it something like SheetCam TNG2.exe. If you run this copy it will be completely independent on the original copy, with it's own settings.
You don't need to install a separate copy. Just make a copy of SheetCam TNG.exe with a different name. You can use any name you like but it must stay in the same directory. SheetCam uses the executable file name to work out where to store it's settings so if you use a different name it will use different settings. The path to the settings will be {application data}\{file name}. For instance if I make a copy called SheetCam2.exe on my Windows 7 computer it's settings will be stored under
C:\Users\les\AppData\Roaming\SheetCam2
You can always find the directory by running SheetCam and going to Help->open settings folder.
SheetCam TNG.exe is just a boot loader (which is why it is so small). The application itself is in camlib.dll. This means that if you install an update your copy will also be updated.
V4.1.10 onwards now have a /pp switch:
/pp "Mach3 plasma"
Note the post name is case sensitive. SheetCam first searches your edited posts. If it doesn't find a suitable post there it tries the main posts folder.