Magento2 Extensions – How to Override a Magento 2 Extension Installed Using Composer

Working solution.

Just create or edit requirejs-config.js file from below path.

/app/code/Namespace/Module/view/frontend/requirejs-config.js

And place below code in requirejs-config.js

var config = {
    map: {
        '*': {
          'Magento_Payment/template/payment/cc-form.html': 
              'Namespace_Module/template/payment/cc-form.html'
        }
  }
};

So we can override any html file in this way.

There are two options here:

1. Described in the comments: create a package or a repository from your extension. If you don't want to push it to the world, you can create a Git repo locally. The repo should contain just your extension and composer.json in the root. Then link your extension's repository as a package to the Magento project in Magento's composer.json (see an example in https://getcomposer.org/doc/04-schema.md#repositories). Use "dev-xxx" version, where xxx is the branch name in your repo - then Composer will always be fetching the latest commit. Then, when you run composer update your package will be loaded with all its dependencies.

2. Leave file structure as is and duplicate all dependencies, autoload and any other deployment-specific information from your extension's composer.json you the Magento's root composer.json. Then when running composer update (in Magento root) all dependencies of your extension will be deployed.