Okay, so the whole "Demo Version" issue is something which quite eludes me. I'm not sure why my code - which works on most installs, by the way - randomly doesn't work, but there it is. After trying a few alternatives I've decided to give up on that feature. I'm releasing the result as v1.8.3.
This version is free of the game-stopping bug where it tells you to buy the full version, despite the fact that you are already playing it. As a consequence anybody who tries to install this on a Demo version of the game won't be able to play it "Shifter-ized" without some extra work and typing things in via the console. If any of you who this applies to can't figure it out, feel free to talk to me and I'll walk you through it.
Anyway, while ModDB approves the file you can download v1.8.3 from here.