I have been working I an migration utility for OpenKM and I performed some changes in jackrabit-core to enable version import, preserving
the modification date. Also modified org.apache.jackrabbit.core.NodeImpl to preserve UUID in the migration process.
This migration process is needed because there are changes in repository node definition, and Jackrabbit can't deal with this actually.
I've attache a PDF with the changes needed in Jackrabbit-core. It works and there was no problems with the migrated repository.