Adding functionality to existing components by extending them and not creating a complete custom component?

[nikolai esla]

The guides and examples are all about creating a custom component, which as the website demonstrates makes sense for slightly more complex components. e.g. The phone number input with 3 sections. However, for simply adding minimal extra functionality, this seems to be an overkill.

Here is an example...

If I want to make a generic, reusable mat-autocomplete, which gathers objects from an API (Service) and displays them, all I should do is to extend the mat-autocomplete. Reason is that it already implements all that MatFormField interface. However, as a beginner I do not see any example/guide out there for this scenario.

I wonder, if there is a design principle discourages from this?