Can I import virtual graph mappings into Designer?

This functionality does not exist yet, but it's on the project roadmap.

As an alternative, you can import mappings via the CLI with the virtual import command. Here are some examples of how to use this command to import mappings:

$ stardog-admin virtual import --format sms2 myDB mappings.sms input.json
$ stardog-admin virtual import myDB source.properties source.ttl
$ stardog-admin virtual import myDB mappings.ttl input.csv

You can read more about importing virtual graphs at our documentation.