There are two methods of 'exporting' metadata. The first is via the Export method (UI and actions). This method exports all metadata in the file. (Artwork is optional with the action method). If artwork is not exported, there will be one file produced per track. This is the best method of capturing all metadata as no knowledge of what 'to export' is required. Nothing can be lost.

The second method involves creating a Track database which contains only the metadata you're interested in. This method can use a single db for your entire collection.

The issue is one of association. The best way to associate method 1, is by having the same file name or by exporting the metadata files with names based on the track numbers. The best way of associating the database items is in decreasing efficiency: Yate Track Ids, file paths, or metadata. You can't use Yate Track Ids as they will not be in the downloaded 'matched' files. 'File Paths' are dicey as the downloaded files will more than likely have different paths or naming conventions. Matching by metadata is not terrible as long as your metadata is reliable and is copacetic with whatever Apple provides.

If the downloaded files can be associated with either method, the restoration is easy via running an action through the Batch Processor. You either do an Import, or find the associated record in the database.

Either way you go, if any....back up!!!!!!! There are far too many horror stories about entire collections being lost.