Is it possible to override an event like a button_click event?

You can have multiple handlers per-event or you can deregisiter and re-register event handlers. In your case before showing the window you would want to deregister the event handler using the -=. If you wanted both to execute (just an FYI), you would add the += and both event handlers would be called (for more information read about chaining delegates).

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Thanks,

Brad