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. Problem is, you may not be aware of which programs could be affected by you editing the registry. So, why not send a message to all the windows notifying them about your action as follows:
SendMessage( HWND_BROADCAST, WM_WININICHANGE, 0, LongInt( PChar( 'RegistrySection' ) ) );
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.
Source : http://www.chami.com/tips/delphi/010797D.html