Is it possible to create a component "addon"?

So, after having done some research and testing various things, I have an answer.

I created a spin-off of my component and stripped it down to the bare minimum. Every file that would theoretically already by included in the core was removed, only the controllers/models/tables/views were kept. Ex: (items prefixed with × were deleted)

/script.php
/administrator
    /controllers
×       /controlpanel.php
        /bulletin.php
        /bulletinlist.php
×   /css
        /general.css
    /models
×       /controlpanel.php
        /bulletin.php
        /bulletinlist.php
    /tables
        /bulletin.php
    /views
×       /controlpanel
        /bulletin
        /bulletinlist
    /controller.php
    /core.php
    /model.php
    /view.php
×/languages
    /administrator
        /en-GB
            /en-GB.com_component.ini
    /site
        /en-GB
            /en-GB.com_component.ini
/site
    /controllers
        /bulletin.php
        /bulletinlist.php
    /models
        /bulletin.php
        /bulletinlist.php
    /views
        /bulletin
        /bulletinlist
    /controller.php
    /core.php
    /model.php
    /router.php
    /view.php

In the manifest file for the installation, it's important to also trim this down to the needed content, and make sure that <extension> has the attribute method="upgrade", otherwise Joomla will cancel the install due to the component already existing.

Important things to note:

• I've tried several different attempts, not once was I able to get the install package to run the install SQL file, I assume Joomla skips this step because this is technically an upgrade. Any SQL changes will need to be done directly in a script.php.
• Any file that already exists will be overwritten, so for things like language files, you'll need to setup a jank solution in script.php to append new JText lines to the end of the installed language file
• In the <administration> section of the manifest file, it's better to remove any reference to <menu> or <submenu>, I've noticed that it will erase whatever menu items existed already to replace them with the structure included in the upgrade

I don't have access to Joomla 4 at the moment to test if this will work there as well, but considering the wording in the Joomla documentation I don't see why it wouldn't work.

Update: After testing some more, I've noticed that any file that is in the root of a folder (/administrator or /site) will be deleted if not referenced in the manifest file. It looks like those files will have to be included even if they aren't different from the core files.