Printer driver port

I have a button that launches an application. before this app is run, i need
to change the port the printer is connected to, and when it is finished
executing, i need to change it back to what it was.

heres the code snippet that runs the app:
case IDC_BTNOPEN:
{
GetWindowsDirectory(lpszSystemInfo,256);
wcscat(lpszSystemInfo,logostr);
_wspawnl( _P_WAIT,lpszSystemInfo, NULL );
}
break;