GP was essentially being a protein-based transpiler. The reference source code was the appropriate legislation; the code GP wrote was transpilation output. Since biological transpilers are slow and error prone, it makes sense to keep the output as close as possible to the input, to allow for "incremental transpiling" ;).

It can still makes sense to translate the rules into a parseable format instead of hard-coding them, to allow for code generation (or dynamic evaluation) and programmatic analysis of the rules.