How simple is it to parse a program in Scheme, with Scheme, into an abstract syntax tree for more complex modification and inspection? Does anybody have a resource for this?

Scheme programs shine at manipulating lists and symbols, and a scheme program is written as a list of symbols. Writing a program generator is trivial. If you know what you're doing, you can write a basic scheme interpreter, from parser to interpreter, in under four hours.

The book "Structure and Interpretations of Computer Programs" is a classic and freely available online.