The Configuration Guide for EAP 7.1 at 7.6.3. "Override Deployment Content" says:
"It allows you to override deployment descriptors, JAR files, classes, JSP pages, and other files at runtime without rebuilding the archive."

However, the actual deployment-overlay feature does not apply to all jar files. It works on jar files located in the lib directory of an ear but not top-level jars in the root of the ear. Thus the documentation is a bit confusing and should be updated.

Perhaps the easiest change would be to replace "JAR files" with "library JAR files" or similar.