become friend and proficient with ALE - Advanced Library Editor.
It will help you export the library, manipulate the output, with some text manipulation (or working with spreadsheets)
Then at the end re-import the changed files and thus updating the library.
Hope this helps
I think his question is how to "updating parts in a legacy design (migrated from DC) with parts placed from our Central Library so that the parts now include all the info now contained in DxDatabook"
If your part still have same name, same partition then an Package with "update6 PDB properties on Symbol" should bring back any property you have in you new dxdatabook. (properties will be also placed if they are defined as common properties and placed in symbol)