This function sets a system value.

#define INCL_WINSYS /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND    hwndDeskTop;  /*  Desktop-window handle. */
LONG    iSysValue;    /*  System-value identity. */
LONG    lValue;       /*  System value. */
BOOL    rc;           /*  Value-set indicator. */

rc = WinSetSysValue(hwndDeskTop, iSysValue,
       lValue);