it would be really helpful for language designers to be able to embed arbitrary C# code in the projection of a token or syntax rule.Yes, it's a good idea in general to stratify the generation of a tree from the postprocessing of its output, but many times it's just far more convenient (and hence more efficient for the programmer) to specify a small transformation function (or even side-effect-causing operation) in the projection of a production.
What distribution are you using?