Creating 'Environment Mask' similar to Sunset Overdrive.


So a bit of context. I’m creating a vertical slice for a university game and I am stuck on creating what is called an ‘environment shader’ in the GDC talk, but I guess it could also be seen as a huge mask for most things in the environment. I am quite terrible with Unreal so talk at me like I’m a baby. There are images with the basic idea I’m trying to achieve however here is the link for what I am talking about:

Heading down to slide 50 is where I start crying. I am trying to create a similar style to sunset overdrive and they have these procedural paint-stroke masks applied to the whole of the environment. I would like to get this in my game but I am unsure if it takes a heavily skilled individual or if someone like myself can achieve this and if so, how? They used their own engine and like I said I am in my first stages of unreal however this would speed up the creation of my game 10 fold. Any help is appreciated!