For purely syntactical changes, you could use build.rs to convert your syntax to standard Rust. It will have issues with source locations unfortunately.
Procedural macros aren't feasible for this yet. If you stick to a syntax close-enough to Rust for the file to tokenize as Rust, you could attach proc macros to individual items. However, having a macro work on entire files or folders is not feasible, because stable proc macros can't create spans for arbitrary files/locations yet.
As for Rust itself, the syntax is stabilized, and won't change. Your best option is to learn how to live with it (get used to it, or use IDE with snippets, auto-complete, etc.).