Думаю, здесь именно "церемониально", а не официально.
"When diplomacy was confined to nearby states and meetings of rulers were easily arranged, a visiting messenger such as the nuncius sufficed. However, as trade revived, negotiations at a distance became increasingly common. Envoys no longer could refer the details of negotiations to their masters on a timely basis. They therefore needed the discretionary authority to decide matters on their own. To meet this need, in the 12th century the concept of a procurator with plena potens (full powers) was revived from Roman civil law. This plenipotentiary could negotiate and conclude an agreement, but, unlike a nuncius, he could not represent his principal ceremonially. "
И, скорее всего, "представлять"