Sagging Rigging

Over the years the rigging on one of my airplanes has gone from taught to droopy. I believe I just used standard cotton thread. Is there any way to tighten this up? I;m thinking about maybe getting it damp and then blowing on it with a heat gun. Something of that nature.



Cutting all the rigging off and replacing it would be a crazy amount of work, and rather difficult since to do it originally I had certain parts running inside the model that are now sealed up.



Thanks for any help!