[CREATURE:EQUIPMENT_WAGON]
[NAME:wagon:wagons:wagon]
[TILE:'W'][COLOR:6:0:0]
[EQUIPMENT_WAGON][COMMON_DOMESTIC]
[TRAINABLE][PET]
[BUTCHERABLE]
[HAS_RACEGLOSS:WOOD]
[ITEMCORPSE:WOOD:NO_SUBTYPE:WOOD:USE_RACEGLOSS]
[NOSMELLYROT]
[BODY:WAGON]
[SIZE:12]
[ALL_ACTIVE]
[NO_GENDER]
[MATERIAL:WOOD:USE_RACEGLOSS]
[TRADE_CAPACITY:15000]
[MUNDANE]
I merely copied a few tags from the domestic file and erased NOT from BUTCHERABLE. I wanted to be able to purchase them on embark as well. Kinda also wanted them to be full scale as you see in game, and not a bunch of brown Ws.
You will have to make a separate wagon entity for the butcherable part, unless you don't really need the trading wagons, then you can just modify the regulars.
First, take off those: [EQUIPMENT_WAGON] [HAS_RACEGLOSS:WOOD] [ITEMCORPSE:WOOD:NO_SUBTYPE:WOOD:USE_RACEGLOSS] [MATERIAL:WOOD:USE_RACEGLOSS] and [trADE_CAPACITY:15000]. Dunno what the [MUNDANE] tag does.
However, if you plan on just butchering them and recieving some substance, you can use the [ITEMCORPSE:WOOD:NO_SUBTYPE] tag - here, you 'kill' the wagon and recieve some random wood. If you feel like breeding wagons, you need to give them genders, thus deleting the [NO_GENDER] tag. From what I see there is no [GENDER_MALE] etc. etc. tag, so if you don't have a [NO_GENDER] tag, the game takes it as granted that you can have...due to inhumane mental images, I'll stay away from an explaination.
You might also want: [LAYERING:700] (or higher, so your new pets don't freeze in the tundra) [HOMEOTHERM:10067] (regular creature temperature) [MAXAGE:80:90] (unless you want wagons that don't die of old age, then just copy the tag off the elves). Oh, and [CHILD:2][CHILDNAME:junior wagon:junior wagons].
Can't think of anything else right now.