Good news, Pastures can be made available for other civs in the Scenario Editor, no data mod needed.
In addition to the effects you already use, you also need to research the internal technology “C-Bonus, Pastures” (ID 1008) for the player. Add the effect “Research Technology”, choose the player, type 1008 under “Item ID”, and tick “Force”.
EDIT: Actually, you don’t even need to enable the Pasture and change its train button location with separate effects. The technology does all that.