In his book *The Silicon Jungle* David Rothman mentions several times the term "modifying" or "customizing" a software program.

e.g. Chapter 8:

*And then the consultant didn’t even supply instructions to operate and modify the software.*

*You could customize the MDBS program in FORTRAN or BASIC.*

Elsewhere:

*You could have WordStar customized for your machine; but why not instead buy a computer that works well with it from the start?*

What does he mean by this? Surely commercial programs like WordStar weren't sold as source code?

Is this modification and recompilation at the source code level? Or is he talking about "configuring".

(Asking this in RetroComputing because the book deals with computing technology from the early-1980s.)