The Windows API function SendMessage() takes a 4 parameters. The first is the window handle. To broadcast to all top level Windows, use HWND_BROADCAST. The second parameter is the message itself, and then the WParam and the LParam parameters for the given message. For the WM_WININICHANGE message, wParam should be zero, and LParam should be either the address of a null terminated section name that changed, or nil if you want each window to examine all sections for the change. Passing a null value is not recommended unless you have modified several sections due to performance considerations. Example:

var
   s : array[0..64] of char;
begin
    StrCopy(S, 'windows');
    SendMessage(HWND_BROADCAST, WM_WININICHANGE, 0, LongInt(@S));
end;