[xwiki-users] Solr schema customization

I would like to customize the solr schema.xml and solrconfig.xml used for our instance of xwiki (enterprise 6.1) to provide some additional fields and to customize (and enforce) search behaviors. My first attempt at modifying xwiki's data/solr/xwiki/conf/*.xml seemed successful at first, but after xwiki restarts the solr index appeared flawed in some way (all search gave zero results) even after full index rebuilds. I see clues in xwiki.properties that custom solr config dirs and even external solr instances are supported, but have not found any specific documentation. I'm not certain the above implies that solr configuration customization is supported. Is it possible and, if so, is there any general guidance on utilizing custom schemas or external solrs? Thanks, Mike