Grade4 tracks hard-coded not suitable for 'car' - what options I have for overriding this

My application is all about creating routes for adventure motorcycling. I have been using my custom OSM data for this and the ‘car’ profile with a custom config.yml. This works great.

I tested a new country (Estonia) and got decent results with out-of-the-box OSM data and my own custom config.file. However, GH does not want ‘car’ profile to use Grade4 tracks at all.

If I wanted to override any part of GH with my own implementation, is my only option to fork the repository and change the car tag parser? I can not see anything like a dependency injection mechanism that would allow me to only create the custom tag parser class, only override the one thing I need (allowing Grade4 tracks) and otherwise use the existing binaries, right?

I noticed a thread from I believe last year about similar sounding “restriction” on bicycle, in which you talked about moving some logic from the bike parser to the json file. Is something like ‘car’ and Grade4 track something similar? Is there a particular reason why this restriction has to be on the code level and not in the profile json files, easily configurable and overridable using the config file?