We have the same issue, since we use Stitch and Stitch does not populate
customs information into ShipStation. Bulk editing products with this
information would also be useful, or adding an automation rule which
handles it on a per order basis.
Not having this option is extremely detrimental to our business. We
don't/can't do things electronically for various reasons and not being
able to print 4 copies of a customs invoice kills our int'l shipping
ability. It's been 3 years, guys.