It should be quite easy to do, can you post a link or picture of what you intend buying, you can buy separate transformers usually called LED Drivers.
You can cut the plug off the fairy lights and connect the lights direct to the driver, but you must choose the correct driver, if you can get a picture of the plug on the lights you intend buying the output information of the transformer should be on there.
I’m assuming the lights are connected in series and the redundant light is the last one in the circuit, having only 1 cable, do all the other lights have 2 cables? It’s not as complicated as it sounds.
Daughters motability car Hyundai Tucson Ultimate self charging hybrid Serenity White Moss Grey interior.
My car SEAT Ibiza SE Tec 1.2 petrol TSI 2017.