Extending an existing rails project
<p>I would like to extend an existing open source rails project (GitLab in my case) by adding/changing views (and controllers). Since the open source project is being actively developed, it would be nice if future changes can be integrated in the new product.</p>

<p>One could simply apply modifications directly on to the original code base. For example, I would like to perform some restyling of the project (to some extent). In this case, I could simply replace all the files in app/views with custom implementations. I could add additional param when a specific action in a controller is called by changing the original code. <em>However, it may become difficult to merge the latest (git) updates from the open source project your personal project.</em></p>

<p>The primary goal is to only implement custom views (keeping behaviour of the controllers/models as-is). However, it would be awesome if the controllers/models could also be extended (in an OO manner) with fallbacks to the original code (perhaps by calling the super methods?).</p>

<p><em>What is the best strategy to extend an existing rails project (views, controllers, models) while minimising the amount of code changes applied to the original project?</em> </p>