I extended some functionality in the slick module, but I am looking to do it in a way that doesn't get erased each time I update slick I extended some functionality in the slick module, but I am looking to do it in a way that doesn't get erased each time I update slick.

I added a css file and edited the slick skin php file to use the css file depending on the user's choice. I also added a bootstrap class to the slick.html.twig template so that the slider would disappear on mobile devices.

Should I make a custom module that acts like slick_examples?
In my opinion, the easiest way to preserve changes to contributed code is to manage your dependencies through Composer and use patches. When you update slick in the future, the output of the command will directly tell you which of your patches have been broken by the update.