Technically that's a subtly incompatible ABI change. ABI changes can be notoriously tricky to spot. That's handled properly on an ELF-based system by bumping the SONAME major (if the library developer knows what they're doing) but that won't help non-ELF platforms or vendored uses.

Of course, the same problem applies in other languages if a constant value changes. A preprocessor macros in C, for example. It's all about non-manifest interfaces and "making things easier" so that any idiot can write software (so they do). Public APIs can be hard when the public is imperfect.