My wife and I did something a little similar. I built out our RSVP system on a web app, but we still printed actual invitations pointing people to go to our website, with a unique handwritten code on each one.
You can check out the code here if interested. It also includes the wedding info site as part of it, so there is a bit of cruft, but I'm sure you could repurpose it if you dug into it deep enough: https://github.com/mvarrieur/vovarrieur-dot-com
For some reason I forget what I wanted this for, but I literally was thinking about trying to find where you could order these things just a couple weeks ago. This is super cool. Good luck!
Yeah so that my Grandma who had Comcast install her router should definitely be legally culpable when there is a firmware issue with the router, or when the installer sets up a weak password (or none at all). I think you are probably speaking from a tech support perspective where you have had to fix systems that haven't been patched for years and that caused issues. Well, most of the population would be screwed by laws like this thru no fault of their own.
You can check out the code here if interested. It also includes the wedding info site as part of it, so there is a bit of cruft, but I'm sure you could repurpose it if you dug into it deep enough: https://github.com/mvarrieur/vovarrieur-dot-com