Picard is a tool to retrieve data from musicbrainz.org and write these to tags.
You cannot create a release from picard, you need to do that from the website.
There are ways of preserving tags see How to preserve all but one or two specific tags
When you add a release to musicbrainz you can specify the release date of that version.
There is the concept of release groups as a level above releases used to group different versions of releases.
The earliest release in the release group is used for the original release date tag so the best thing to do would be add the earlier release group to the database.
There is scripting support that could copy tags around but that is probably the wrong way of doing things.