replacing instance of class from within itself

Hello Friends,

This one is a bit weird I feel :) I have a class which defines goals for a level. Mostly checks on multiple counters. As the system allows for quests to be chained, every LevelGoal has a ChildGoal.

This looks like following:

 public class LevelGoal
 {
         private bool isFullfilled;
         private int goalIndex;
         private int amount = 0;
         private LevelGoal childGoal;
         [...]

when a goal is fullfilled, I update the hud and everything. But what I would like to do is override the current instance of the LevelGoal with its child if not null - this way, all other game components wouldn't have to care whether there is a child task or not.

basically, what I'm looking for is a "legal" and safe way to say:

                 if (isFullfilled) {
                         hud.resolveGoal (goalIndex);
                         if (childGoal != null)
                             this = childGoal;
                         else 
                             return true;
                }

hud works fine, childGoals work but I have to access the childGoals manually to check the progress instead of letting it replace the parent.

Any tipps/followup readings and comments are very welcome!

Thanks a lot, Georg