If you change a registry entry that is being used by another application, it's a good idea to let that application know what you did so that it's able to update / refresh itself.
Just notify all running applications by sending a message to all the windows about your action as follows:
SendMessage(HWND_BROADCAST, WM_WININICHANGE, 0,
LongInt(PChar('RegistrySection')));
"RegistrySection" is of course the registry section which you changed.
If you're using Windows 95, you may have to use "WM_SETTINGCHANGE" message instead of "WM_WININICHANGE."
Also, it's possible to use Win32 API function "SystemParametersInfo()" to send out more specific notices about registry and/or system parameter changes you make