"To borrow your analogy of the can of worms module, that it runs well but will become a bomb as soon as someone decides to rewire it fills me with a sense of deep dread. My mind immediately drifts to the scenario where something forces changes on that module, such as the server continuously crashing due to a latent schrodinbug that just surfaced, but in a time-frame where those 47 issues just can't be resolved. I've never been comfortable with the justification that "it works now, so just don't screw with it." It seems to just be begging for Murphy to make a fool of the person justifying a decision thusly."

Yes, so you make that part of the decision. It's all contextual; you can fiddle with this hypothetical this way to make it 'yes', you can fiddle with it the other way to make it 'no', and both hypotheticals will be simplified to the point of irrelevance compared to any real situation that may arise.