it’s about deploying multiple versions of software to development and production environments.
What do you think a package is used for? I mean, what do you think "delivery" in "continuous delivery" means, and what's it's relationship with the deployment stage?
Again, a cursory search for the topic would stop you from wasting time trying to reinvent the wheel.
https://wiki.debian.org/DebianAlternatives
Deviam packages support pre and post install scripts. You can also bundle a systemd service with your Deb packages. You can install multiple alternatives of the same package and have Debian switch between them seemlessly. All this is already available by default for over a decade.
That's a huge security problem.
Edit for those who are down voting this post, please explain why you believe that granting anyone in the organization full access to all the projects used across all organizations does not represent a security problem.