Seems you have a solution.

Bur if not, some ideas.

The price you paid for the shipment and customs was for the whole shipment, a big box with a wheel and the two Supernova lights in their huge metal boxes.

For the replacement of the tail light, you just need the tiny rear light that without the big Supernova luxury packaging is very small, weight about nothing and fits in an envelope.

So shipment costs should be very low.

Since it is a replacement part of a previously imported tail light for which you paid customs, you can declare it as such with a zero declared value.

UPS does the import custom clearance themselves and its possible to declare the gods as said above to them.