How customizable are these textures?
The substances are incredibly powerful, with many features that allow for a large amount of options and changes. Even these however can be limited.
Some of our textures are not procedural however and will require more work in engine or in a photo manipulation program.
There is no general rule as to how much you can customize these materials as they are, however you are encouraged to use them in your texturing programs or game engines in ways that will get the most out of them by any way possible.