Is there a way to change which trainwagons spawn?

[RustMaker]

On a map with tracks, the workcart and trainwagons will auto-spawn.  I am looking for a way to limit which trainwagons (there are 4 or 5 types) will spawn down to a certain type (trainwagona.entity).  Is this even possible?

[Death]

I believe you're looking for:

traincar.wagons_per_engine Ratio of wagons to train engines that spawn (2)

All the other convars:

vehicle.cinematictrains  If true, trains always explode when destroyed, and hitting a barrier always destroys the train immediately. Default: false (False)
vehicle.trainskeeprunning Determines whether trains stop automatically when there's no-one on them. Default: false (False)
traincar.population      Population active on the server (0.6)
traincar.wagons_per_engine Ratio of wagons to train engines that spawn (2)
traincouplingcontroller.max_couple_speed Maximum difference in velocity for train cars to couple (9)