If a replacement library is specified on the URL, it will override any other replacement library setting for that library. If specified as a user property, it will override application and WOW global replacement libraries. And finally, application replacement libraries will override WOW global specified replacement libraries.
For Example:
Let's say the application was run with a URL parameter _pj_replace_libs=LIBRARY1=REPLACEMENTLIBRARY2. In addition, we'll say that there is a replacement library specified on the application being run. (Config {replacement libraries: LIBRARY1=REPLACEMENTLIBRARY4 ;}).
When an SQL is run, REPLACEMENTTABLE2 would be used because URL replacement libraries take precedence over application replacement libraries.