Need a connector for a particular use.

[JerseyMatt]

Are Christmas lights UL listed by the entire strand? (Pulling a bit from another thread, but also curious since I can conceivably see having to do something like this myself in the future) Wouldn't modifying it in this manner void the listing?

Yes it would. Cutting/modifying any wiring on a UL listed assembly voids the listing. This even applies to when you have to replace a broken plug on an extension cord or instrument.

The better solution to the OP's problem is to use shorter strings of lights and arrange them so the end-to-end connectors line up. Or else roll the dice and risk the FM shutting him down.