There's a sh_config.lua inside the gamemode. You need to unpack the mod, edit it and repack, or just download the mod from github (create a zipball from master) and edit the file and copy anything to Gmod's folder. Maybie is easyer to edit from console this var:
// Props will not be able to become these models
BANNED_PROP_MODELS = {
"models/props/cs_assault/dollar.mdl",
"models/props/cs_assault/money.mdl",
"models/props/cs_office/snowman_arm.mdl"
}

thanks for the quick reaction

Greetings
Wesley