I’ve now got @sbaio’s Zellen script working with the Shield and Launchpad, so I thought I’d give a quick overview of the process, in case it’s of any use to anybody:
In maiden:
01 Install Zellen from the available community scripts list.
02 Find Zellen in Files > Code, click to expand, then click zellen.lua to edit.
03 Scroll down to the entry for local g = grid.connect() and insert a new blank line above.
04 Enter this entire line: local grid = include("midigrid/lib/midigrid")
05 Save the edited script.
Shut down the Shield, hook up the Launchpad and restart the Shield.
Set Launchpad’s display to Programmer mode.
Load Zellen and adjust parameters to taste (the readme is the place you should look for all of that info - there are loads of things that can be changed!)
Activate some cells on Launchpad, hit K2 on the Shield to play - and be ready to lose a couple of hours experimenting! 
I have put a short video over at my Insta to give an idea of how it looks.
I feel like I’ve been monopolising this thread lately and will probably butt out for the time being (I’ve been from A to Z (literally!) in the scripts) - it’s been quite a trip so far, and I hope my notes on my early explorations into using a Monome Norns Shield with a Launchpad Mini Mk3 can be of some use to somebody.
@Chico - I’m happy to hear you’ve been able to fix the audio out issues, and I hope you enjoy the ride from here on out! 
@DoS - Thank you yet again for all the info, I really do appreciate it. It’s looking more and more likely that there’s going to be a second Launchpad in my future! 