Any tips for creating language plugins with existing grammar files (or, without Grammar-Kit)?

I have created a toy language in Rust and want to focus on making its IntelliJ plugin as the main option for developer experience.

But I have an existing grammar file in Pest (https://pest.rs), and I found it kinda undesirable to keep multiple grammar files in sync. So are there any tips or other options for creating such plugins without the classic Grammar-Kit generation-based pattern?