Even after TRC OK, not aware of any process that relieves the airport personal from their check-in responsibilities. UA agents use Timatic and you can do trial run at https://www.united.com/en/us/timatic and see if you situation is covered. You can then guide the airport agent to the right section.

Purchasing a refundable return with 90 days, may alleviate checkin issue and entry the destination country with the special entry items.