How to introduce a new pattern into an existing codebase? [duplicate]

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• How to measure the potential value of refactoring 7 answers

In my quest to better my development skills I learn new design patterns. In sample projects or personal projects it's really easy to adapt new patterns into my code.

However at work I have a large code base that I am responsible for architecting and maintaining. This question is focused on writing consistent and maintainable code will still providing business value.

When I learn new patterns I find myself conflicted on how to proceed moving forward on an existing codebase.

Do I go back update my code to use my new pattern ?

• This has the downside of not providing a ton of business value and might not be the best way to efficiently utilize my time.

Do I move forward and use my new pattern/technique in any new code ?

• This has the downside of being inconsistent, thus making my code less maintainable and setting a poor precedent for new team members.

Optionally I could just catalog the new technique in my head but not implement it. I really dislike this option though.