“external_login_url” customize login_form

I need to customize Plone login form without make changes in plone original login-form https://github.com/plone/Products.CMFPlone/blob/master/Products/CMFPlone/skins/plone_login/login_form.cpt i think there are two ways one way is to use override.zcml to change login-form and a simple login.pt file :

   <browser:page
    for="OFS.interfaces.IApplication"
    name="plone-root-login"
    class="Products.CMFPlone.browser.admin.RootLoginRedirect"
    permission="cmf.ManagePortal"
    template="templates/login.pt"
    />


Traceback:
 File "/Plone/buildout-cache/eggs/Products.CMFPlone-4.3.3-py2.7.egg/Products/CMFPlone/browser/admin.zcml", line 43.2-48.8
    <browser:page
        for="OFS.interfaces.IApplication"
        name="plone-root-login"
        class=".admin.RootLoginRedirect"
        permission="cmf.ManagePortal"
        />
        File "/Plone/buildout-cache/eggs/my_app/my/app/browser/overrides.zcml", line 7.4-12.10
      <browser:page
          for="OFS.interfaces.IApplication"
          name="plone-root-login"
          class=".admin.RootLoginRedirect"
          permission="cmf.ManagePortal"
          />

And Second one to set external_login_url in default/propertiesTool.xml i tried but changes not reflected.So what to do please tell me ???

I must not understand. When you customize the login form you're not changing the original; you're just telling Plone to use your version. What's the underlying problem you're trying to solve?

Thanks @tkimnguyen actually i was trying to tell plone to use my login form by using override.zcml instead of using origin one but it through an error