I don't see why you can't use the brushes to make things. Case in point... All graphic programs come with a selection of brushes, shapes and tubes, and you can use them to make things. So I don't see why you can't use brushes that you have bought or obtained for free to do the same. That's the entire point of a brush.. to make things. No point in having them if you can't use them.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi