Answer
Yes — the External File Assistant's supplier-invoice file type supports a separate Posting line type in addition to the Header and Invoice Line types; each posting row needs to be linked back to its invoice via the invoice number, the same way the invoice lines are. Structuring your import file with all three line types (Header, Invoice Line, and Posting), correctly tied together by invoice number, lets a single import create both the invoice and its full posting/accounting distribution in one step.