Only the fields shown in C1 are enterable/editable in C1.
However if you turn on XMP syncing in the preferences you can use any XMP compliant software to enter whatever metadata fields those software packages support.
You won't see the result in C1, but C1 will not remove/write-over them in the course of XMP syncing.
Depending on the size/scale/cost of your operation you may consider Capture One Consultation
which could include coding of a custom solution to pull and enter metadata from a database, excel spreadsheet, barcode scanner etc. Depending on the complexity of the workflow that could be anywhere from 2-5 days of consultation time. It wouldn't make much sense for a single photographer who is just trying to avoid copy-pasting while shooting 1000 products over a week of shooting; but would make sense if you're managing a studio with a half dozen shooters working year-round doing the same redundant data entry.