Magic on Earth-at-the-End

I've been thinking a lot about Magic on Earth-at-the-End, specifically in the form of Lighthouse Cults.  The cults and their devotion to the mysterious orbital installation which is so large it can be seen from every part of the world's only continent and in daylight.

I hadn't intended Earth-at-the-End to be a B/X setting, but I've been using Necrotic Gnome's B/X Essentials books for inspiration and templates for monster stats.  The Essentials books are my gold standard for reference because they're laid out so well.  The cleric and magic user spell lists work well for my setting, because they lend themselves to reskinning as technological effects instead of supernatural ones.

My basic premise is that magic is ancient technology in a convenient, portable form.  (Cure Light Wounds?  It's a ray that reverses entropy in a limited area.  Originally intended to keep meat fresh for consumption.)  Handed down from parent to child or from master to apprentice.  It's not something you learn, it's something you inherit.  Magic-users are machine operators who understand their devices well enough to aim and trigger them, but not the underlying principles.  Spells can occasionally be created anew by salvaging a piece of technology and making it portable -- maybe the Last Academy has a few painstakingly-copied manuals that describe those devices well enough to identify them and a few reliable techniques for swapping out power sources and control plates.  Perhaps there's a crazy Godmind out in the desert with a cult of dedicated followers worshipping in a machine workshop.

Following on from that, anyone can use these devices but only magic-users have the training to use them correctly and in a crisis.  And devices aren't restricted by level, but the knowledge to use them properly might be.  I think it would be a useful rule to have the user roll 1d6 and if the result is equal or less than the difference in levels between device/spell and user, the attempt is a mishap on the following table.  Non-magic-users take an additional -2 penalty.

1. Reduced effect.
   The device functions as intended but the most important factor (potential, range, area of effect, number affected, save difficulty) is reduced by half.
2. Increased effect.
   The effect goes off as planned, but too much.  A medical device might treat the target's mouth as a wound to be healed over.  A single-target weapon might gain an area of effect.  A charmed person may become obsessively protective of the user.
3. Reversed effect.
   A healing device harms, a transport device roots the target to the spot, charm becomes grudge, etc.
4. Random target.
   Roll 1d8 and whoever is nearest in that direction from the intended target (and within range) becomes the device's new target.

Example: Barret the technician(1) attempts to help an ally who has been exposed to an ancient virus by using a Cure Disease device.  It's a 3rd-level device, so the difference between his level and the device's is 2.  He rolls 1d6 for mastery and unfortunately the result is 2, a mishap.  He rolls 1d4 and gets 2 again: Barret's device kills the virus in the ally's body, but also a great deal of his normal intestinal bacteria.  The ally's next meal will make him vomit.

I'm giving some thought to combining the cleric and magic-user spell lists.  Earth-at-the-end is a tired and cynical place, and the only faith you'll find is the lighthouse cults' hysterical need to believe something can save them when the world ends.  Organised religion is a thing of the deep past.