Seems a little on the nose, but I do agree, stuffing this specific thread with trying to understand how to mod isn’t the greatest of ideas. (even tho learning to mod is good) You can always ask somewhere else though. Maybe try reading the documentation or watching some tutorials? (But PLEASE don’t watch the one from like 2017 why does everyone use it then stuff up bc they used a .cs file instead of a .json file aargh) ..sorry got a little off-topic myself.
They probably have no intention of adding it. Plus, that would require a new model where lots of new parts would have to be converted/ made for the wagon body.