To gradually adopt Harmony while reusing existing features in a project, developers can transform apps into dependencies by wrapping them as Bit Components, which allows for the composition of functionality across projects. By signing up for Bit Cloud and creating a Scope to store these components, developers can manage their existing apps as Bit Components with tools like Create React App. This involves setting up a Bit Workspace, configuring entry points to expose internal features, and using the `bit add` command to track the app. Once released on Bit Cloud, these components can be reused as packages via Bit or other package managers, with the flexibility to expose more features and automate the process using CI tools. This method enhances the developer experience by preventing direct imports of internal files and improving documentation.