The ResUtilAddUnknownProperties utility function adds unknown properties for a given object to the end of a property list. Unknown properties are properties that are specific to a resource, but foreign to the resource DLL.
DWORD WINAPI ResUtilAddUnknownProperties(
  PVOID ClusterKey,
  const PRESUTIL_PROPERTY_ITEM PropertyTable,
  PVOID OutBuffer,  
  DWORD OutBufferSize,  
  LPDWORD BytesReturned,  
  LPDWORD Required  
);
 
If the operation was unsuccessful, ResUtilAddUnknownProperties can also return a Win32® error value.
ResUtilAddUnknownProperties supports unknown properties by reading them directly from the cluster database without involving the resource DLL, thereby allowing a resource to be extended by another resource or an application. Unknown properties are considered private properties; unknown common properties are disallowed.
  Version: Use Windows NT Server Enterprise Edition 4.0.
  Windows CE: Unsupported.
  Header: Declared in clusapi.h.