I think the biggest drawback is if you ever decide to sell the car.
Next owner might not take kindly to failing emissions for a non refereed "engine change" and the shops you know may not take kindly to you selling a car on a sniffer test they slipped through for you
Next owner might not take kindly to failing emissions for a non refereed "engine change" and the shops you know may not take kindly to you selling a car on a sniffer test they slipped through for you