With Leaptest its very rare that you would be required to add custom validations, but if you really need that then you can call CMD or PowerShell from Command Line block and execute your custom code.
If you can run the program on the screen, you could drive it “visually”. But this would probably be more suited for an upcoming feature we’re working on called “Code blocks”, which, as you might imagine, allows you to write custom building blocks using code. We’re evaluating possibility of having code block and it might get release in early 2018.
For any clarification, please contact our Priority Support.