Site lib/
EPrints 3 Reference: Directory Structure - Metadata Fields - Repository Configuration - XML Config Files - XML Export Format - EPrints data structure - Core API - Data Objects
site_lib/ does not exist by default but is a special directory which allows direct overriding of Perl modules under perl_lib/. E.g. If you wanted to change the code in perl_lib/EPrints/DataObj/EPrint.pm, you could copy it to site_lib/plugins/EPrints/DataObj/EPrint.pm and edit it there and the latter version would be loaded in place of the former.
site_lib also allows adding of code and configuration using the same path structure as used in lib/. E.g. If you already had a file at lib/cfg.d/my_config.pl, then if you created another file at site_lib/cfg.d/my_config.pl this latter file would load in place of the former.