We have made some customizations to /usr/share/koha/intranet/htdocs/intranet-tmpl/prog/en/xslt/MARC21slim2OAIDC.xsl They are silently overwritten on every upgrade, which I avoid with dpkg-divert. Since there is more than 30 XSLTs on that folder a syspref solution might be hard. An easy solution maybe is, instead of overwriting ask the user what to do (stop the upgrade and wait the answer): Configuration file `/usr/share/koha/intranet/htdocs/intranet-tmpl/prog/en/xslt/MARC21slim2OAIDC.xsl' ==> Modified (by you or by a script) since installation. ==> Package distributor has shipped an updated version. [...] *** MARC21slim2OAIDC.xsl (Y/I/N/O/D/Z) [default=N] ? Marking them as conffiles as the others (dpkg --status koha-common). Or even always preserve conffiles. User can always overwrite with dpkg-reconfigure or sudo apt-get -o Dpkg::Options::="--force-confmiss" install --reinstall koha-common BTW, I don't know why this XSLT is on a LANG folder, since always use «en» (bugs 4403 and 10292).