To initialize a JavaScript component using a data attribute, the developer should use the data-mage-init attribute. This attribute allows the developer to specify the name and configuration of the component in a JSON format. For example:

This will initialize the nav component from the Vendor_Module/js/nav file with the given options. The data-bind and data-init attributes are not valid and will not work, as they are not supported by Magento. References: [JavaScript initialization], [data-mage-init]

The best way to customize a template file from a third-party module is to create a new theme that inherits from the parent theme and override the template file in the app/design/frontend/Custom/Theme/Vendor_Module/templates directory. This way, the customization is isolated from the original module and can be applied to a specific website or store view. Creating another layout file or a new module would not be as simple or flexible as creating a new theme. References: Frontend development guide, [Create a theme], [Theme inheritance]