Possible to add another item to an existing enum type?

I wonder whether it is possible to add/append another item to an existing enum type (part of a framework)?

Something like this: We have the enum type

  typedef enum {  
    UIModalTransitionStyleCoverVertical = 0,  
    UIModalTransitionStyleFlipHorizontal,
    UIModalTransitionStyleCrossDissolve,
    UIModalTransitionStylePartialCurl,
 } UIModalTransitionStyle;  

Now I want to append or add to this set an item like UIModalTransitionStyleCoverVerticalFlipped. Can something like this be accomplished?