Sort of.  They are declared `const` in the `omero::callbacks` namespace without being `extern`.  So they are visible, but will be local to the translation unit including the header.  That is, there will be no global symbol by that name (I've verified this running `nm -CD` on libomero-client.so).  So there is no ABI change, but it will be an API change should anyone have any reason to use these constants.