How about the database?

For Daz products, and soem products from other stores, you can reimport metadata - that will also catch any of your own metadata (recategorisations and your saved files) from before the last time you did an export userdata (if you did). The database on the old system will have everything that was, but it isn't possible to directly merge that with the dataabse on the current system so you risk losing metadata assigments either way with that.