title: override paperclip has_attached_file settings that were set in a gem
body: <p>In my project i have a gem that uses paperclip for file attachments. an example model in the gem:</p>
  
  <pre><code>class Example do
  ...
      has_attached_file :image,
        styles: { mini: '32x32&gt;', normal: '128x128&gt;' },
        default_style: :mini,
        url: '/example/url/:id/:style/:basename.:extension',
        path: ':rails_root/public/example/url/:id/:style/:basename.:extension',
  ...
  end
  </code></pre>
  
  <p>I want to modify the image so instead of having <code>mini</code> and <code>normal</code> sizes, i can add another size. I also want to change the path. How do i go about this? i tried creating a decorator like:</p>
  
  <pre><code>Example.class_eval do
      has_attached_file :image,
        styles: { mini: '32x32&gt;', normal: '128x128&gt;', large: '1024x1024' },
        default_style: :mini,
        url: '/example/url/:id/:style/:basename.:extension',
        path: 'updated/example/url/:id/:style/:basename.:extension',
  end
  </code></pre>
  
  <p>this didn't do anything. </p>