gistfile1.txt

Basically, http://docs.plone.org/develop/addons/components/zcml.html#specify-files-and-code-from-another-package explains how to do it. But the example is not very clear, since in both cases the same packge is referenced. Therefore, a simple example:

Suppose you want to overwrite the folder_contents view in Plone. You only need to change some code in the class and you're happy with the template.

The view is defined in plone.app.content.browser with this zcml statement:

<browser:page
    for="Products.CMFCore.interfaces._content.IFolderish"
    class=".folder.FolderContentsView"
    name="folder_contents"
    template="templates/folder_contents.pt"
    permission="cmf.ListFolderContents"
/>

In your own package, you create a class that extends FolderContentsView and performs whatever additional magic you need. To use your own version of folder_contents with your own class but the original template, you can add this to your package, which in this example is called "my.package"

 <!-- override folder_contents -->
<configure package="plone.app.content.browser">
    <browser:page
        for="Products.CMFCore.interfaces._content.IFolderish"
        class="my.package.browser.foldercontents.MyFolderContentsView"
        name="folder_contents"
        template="folder_contents.pt"
        layer="my.package.interfaces.IMyPackageLayer"
        permission="cmf.ListFolderContents"
    />
</configure>