You can just move the Substance plugin from marketplace folder (from stock 4.19) into your UE4 projects Plugins folder, make sure you have c++ project and then regenerate the project files from .uproject. will generate a visual studio solution which lets you compile substance for the engine version you are using for the project.
I will not add substance plugin in my own merged repo as it breaks UE4 EULA, while it’s a free plugin UE4 marketplace, it’s license doesn’t give me rights to redistribute the source code so I can’t do it myself.