The 1.7.10 version had the ability to disable weeds. Is it possible to get that configuration and associated behavior back into the versions for the newer releases of MC?

check the json files for the plants. Specifically: config/agricraft/json/defaults/plants/weed_plant.json

Change the value for enabled to false.

This could definitely be made more obvious, but this is already possible

Changing the JSON file is correct. There are no longer weeds proper like in 1.7.10 to be disabled through config.