My use case:
I have a collection of items in a group library I once created for a collaborative project. Once the project ended, I would like to integrate the items into my private library and delete the group library.

I see two ways to do so:
1. I can move the items or collections by mouse or
2. I can export the library as zotero-rdf and import it into my personal library

Both ways result in new entries that maintain the information and added notes, pdf,... but the entries get a new timestamp for "added on" ("Hinzugefügt am") and "change on" ("Geändert am") with the time/date of the moment I move or import them.
This behavior might be logical and wanted if I import an item from some external source, and in fact it is the first time I have the item in my Zotero database.
In my case of reordering my entries between group and privat library it is not what I want (although I understand, that technically my group library is external to my private library and I do copy an item and don't simply move it). To me, it is sometimes important to know when I entered the information into my database. I would like to maintain at least the "added on" date from the original group library, it is ok to have the "changed" timestamp set to the date of moving the item around.

So my question is:
is there a possibility to move items from a group library to a private library and maintain the timestamp as it would be, if I move around an item within one library? Maybe some hidden configuration setting to activate? Like it is possible to select that the im-/export includes notes and attachments or not.