[Radiant] change action through extension

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I want to change the action where in controller,  for example:

/radiant project/app/controllers/admin/pages_controller.rb    has one
'index' action

def index
    @homepage = Page.find_by_parent_id(nil)
    response_for :plural
  end

I want to change it to:

 def index
    @homepage = Page.find_by_created_by_id(current_user.id)
    response_for :plural
 end

But how can I change it through extension/

thanks
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