James:

I think this project is caught in a legacy trap. Although it looks and feels like a device that you would hold in your hand, in practical terms, why would you ever do this?

A legacy meter would be grasped tightly as you watch the display, but in this case the box itself will most likely be dangling on the end of the cable or wedged in a cabinet. Thus I see no safety concern in opening the slot.

If one was to hypothetically do this they would find it a bit of a challenge. Although the wall is thinned quite a bit the material is rather tough and requires patient shaving layer by layer. Hypothetically of course.

Tom