No no. Well, it isn't my field of study either, it's from what I recollect of 1st yr UG! When you cross the yield point, deformation is plastic. Plastic deformation means deformation is permanent. In elastic deformation the material retracts to original length. Now, I bet any form of heating of human tissue *may not* cross it's yield point. So it may be somewhat near the yield point, which means deformation is partially plastic and partly elastic. Another factor in human tissue is healing. So keeping tissue stretched will trigger the healing mechanism to fill the voids caused by microcracks. I think that's the theory of [words=https://shop.mattersofsize.com/products/sizegenetics-penis-extender]traction[/words] right? And mind you, plastic deformation is also caused by microscopic tears in the material. Only thing is that a non living tissue won't heal...
So to answer your Q, heating with stretching might *slightly* reduce the yield point of the tunica (dunno length or girth). The *slightly* is because as I said, owing to the poor thermal conductivity of the penis, the temperature at the tunica will be fairly low, even if it felt hot in the outer skin. But you say type-I collagen is unstable at even body temp. So then the heating might work!!