I like to use a flexible silicone scraper to stir my eggs in the pan when scrambling them. I know silicone is heat resistant so it won't melt, but will prolonged exposure to heat gradually cause the silicone to harden and become less flexible?
First, you need to be sure that the scraper or spatula you are using is heat resistant and suitable for cooking.
Assuming it is, heat should not make the silicone hard over time. I have several that I have been using almost daily for over ten years. They are as flexible today as when they were new.