Is there also a way to extend the App_Plugins\Vendr\package.manifest with extra javascript registrations? Is there something similar for the manifest file, like with how the analytics dashboard config can be overridden by adding a file {my-proj-name}.analytics.dashboard.config.js?

Edit: Made it work using the following setup:

• Added the following config file App_Plugins\Vendr\Config\foobar.analytics.dashboard.config.js to override the dashboard config.
• Added a new folder App_Plugins\VendrExtensions\
  • Added my controller extension like App_Plugins\VendrExtensions\backoffice\js\analytics.controller.js
  • Added my widget views under App_Plugins\VendrExtensions\backoffice\views\analytics\widgets\
  • Added package manifest under App_Plugins\VendrExtensions\package.manifest

package manifest:

json 
{
    "javascript": [
        "~/App_Plugins/VendrExtensions/backoffice/js/analytics.controllers.js"
    ]
}