Keep in mind that the synthetic nature of the fabric could be an impediment if you use high temperature, read the specifications if present or look for it knowing the precise material, which probably would be some kind of fiberglass cloth. What kind of use are you thinking about? It a nice idea to use an incandescent xmas rope to provide bottom heat to the cuttings and keep them growing or at least out of dormancy. Although If the minimum temperature in the area where the plant is located is very low I recomend you to let the plant go into dormancy and keep it inside home, because the thermal shock could be more damaging if the sap is artificially moving through the tissues.
God luck from Spain!

You can use the small incandescent mini lights. Its unlikely they will produce enough heat to risk fire. I think each mini bulb is about a half a watt and can be touched after being on for hours.

I wouldn't worry about heat starting a fire (check out the
Mythbusters show on Xmas trees). Heat alone won't
cause a plumeria to burst into flames.

Xmas lights will help, but don't use the new LED bulbs,
the provide almost no heat at all. I'd use C-6 or C-9
bulbs. Mini-lights (AKA Italian lights) won't provide much
heat at all.

I use indoor/outdoor "Italian" incandescents under the frost cloth. Lay the string on the ground looping around and under the plants, cover with frost cloth.

My experience has shown a c-9 bulb will melt certain synthetic materials if the bulb is in contact with the material. Which is what I understood the OP was concerned about.

Melted plastic on C9 bulbs