By that I mean a way to configure the already existing fuels (gasoline, diesel, biodiesel etc.) to configure their speed, stress, burn rate.

Gasoline, diesel/biodiesel, have the same stats and it would be nice if they are changed or if you could modify them in the config. In real world they work a bit different, so you could make gasoline have a higher speed and burn rate, but lower stress, and the opposite for diesel/biodiesel.

You can turn off forge:diesel, forge:gasoline and forge:fuel in the configs, and add the createdieselgenerators:diesel_engine_fuel_[slow/fast]_[strong/weak]_[slow/fast]_burn tag to them I guess