Let me know if it works for you, even if you run into the server restart problem. If that's good BE code, I'll put in into the OP.Haven't attempted it yet but plan too later tonight.
I've researched and found that dayz.st servers do not allow you to change the server.cfg. causing the createvehicle.txt to be wiped free of any changes each restart. Not sure if this is true since I have never manipulated the createvehicle.txt myself.
I think the guys at dayz.st will change it for you more permanently if you contact them, but ultimately you'll probably want to get a dedicated server or someone who allows access to everything.