1- how to put the file in /etc/ of installation directory (in discussion)
2- how to allow the perl script (from staff interface) to write or rewrite the yaml configuration file if a librarian decides to change some settings.
If I do nothing special, YAML::DumpFile fails to (re)write the file, because - I suppose - the apache user does not have rights to access the server.
So, for the moment, the only way I found to make my config file editable is "chmod 666".
But I suppose it is not very safe...