title: How to override/replace the related field from base in odoo 9
body: <p>Existing Field(base addons):</p>
  
  <pre><code>journal_id = fields.Many2one('account.journal', related='statement_id.journal_id', string='Journal', store=True, readonly=True)
  
  New Field(custom addons):
  
  journal_id = fields.Many2one('account.journal',string='Journal')
  </code></pre>
  
  <p>I want to change the existing field into new field like above example.</p>