So I've realised that if only the Publish Blog is being read, it's really only telling half the story regarding IMDL! There's a lot more detail on the Design Blog regarding my trails and tribulations but in summary, I've managed to find a workable solution to my design problem. That being multiple dice (each mod gives the player 1 or 2 customised dice instead of a configurable face).
This has involved a fair amount of rework with the mech mods and enemy cards, mostly around the balancing. Play testing continues but it certainly captures the original feel.
Customisable dice are a lot easier to come by so I'm happy I can continue! If you're interested in the journey, click over to the Design Blog.