Shared messages are in one file.

And your ignoring the issue of promoting these changes through the environments. Until you understand that, all of this is really hand-waving.

You're adding nothing other than overhead.

Your approach would take longer because you have to open and close each file/screen that needs a change.
It might if that were an actual change that occurred. You're inventing problems. Or let's say you're not. Let's say that someone actually comes up with that change, once. WHO CARES? You're adding overhead and complexity for one lousy change that might happen once. Sounds like a pain in the ass to me.

And are you going to concede that we aren't exactly unfamiliar with databases and their uses here?