This plugin adds some extra fields to ArchivesSpace EAD and MARC exports based on user defined fields.
Built for Dartmouth college and developed against ArchivesSpace 1.2.x (although should run against 1.3.x as well)
The usual:
cd /path/to/your/archivesspace/plugins
git clone https://github.com/hudmol/dartmouth_udf_exports.git
Then edit config/config.rb and add the plugin to the list:
AppConfig[:plugins] = ['local', 'other_plugins', 'dartmouth_udf_exports']