A: Absolutely! WordPress hooks (add_action, add_filter) are a perfect OCP implementation using procedural code. Your functions stay closed (working code), others extend via hooks (adding functionality). OOP adds more tools, but hooks alone achieve OCP beautifully.

A: Initially yes, but it pays off as the project grows. Start simple – a few hooks are enough for small plugins. Add interfaces and abstract classes when you have 3+ similar implementations. The complexity is justified when it prevents breaking existing functionality while adding features.

A: OCP is crucial for plugin compatibility. If your plugin follows OCP (provides hooks), users can extend it safely. When you update, their extensions keep working because they’re not modifying your code. This is why editing vendor plugin files is dangerous – updates erase custom changes.

A: Add hooks at logical extension points – before/after major operations, when data changes, or when rendering output. Follow WordPress core’s approach: do_action('before_save_'), apply_filters('the_content'), etc. Don’t overdo it – too many hooks make code hard to follow.

A: No, only functions that return data users might want to modify. Use filters for content transformation (apply_filters('post_title', $title)), use actions for event notifications (do_action('post_saved', $id)). Internal helper functions don’t need hooks.

A: No, OCP is about adding features, not fixing bugs. Bug fixes are legitimate modifications. The principle means “don’t modify working code to add new features” – fixing broken code is different. After the fix, that code should be closed for new features again.