@sympatik , keywords are: lerp (linear interpolation) dynamic material instance material parameter Thats for unreal. I think in unity you have to write a shader, but I dont really know. It's a lot to learn, but it's all stuff well covered by many tutorials and documentation.
that is a programming question, and there are many answers. what game engine you using? You should probably ask on the forums for that engine. If it's unreal, you can lerp between two textures and drive the change via a parameter you get access to from a dynamic material. That is all steps covered by thousands of youtube…