[flexcoders] Possible to edit and recompile Flex framework?

[zzwi89]

I am running into an issue where the HistoryManager is referencing a
null object and throwing an error (see:
http://tech.groups.yahoo.com/group/flexcoders/message/63423). It
appears to be on line 127, in the unregister function:

public static function unregister(obj:IHistoryManagerClient):void
{
    impl.unregister(obj);
}

I cannot simply override a manager, but as this is a null object, I
wonder if a simple fix could be to do a null check against impl and
obj in this function. Although I can figure out how to do this, I
can't figure out how to recompile the entire framework. 

I know this could be dangerous, but there doesn't seem to be any other
fix.