Help! Can i make a civ that uses Spy to drop Amenity in other civs?

[OtsefinamTsinummoc]

I want to make a civ that uses a Spy effectively. The idea is, if a spy is operating in another city, then their Amenity drops -1 per, like, 15 turns and multiple spys shouldn't drop Amenity more than -1 and miximum is like -5 max. Is it only possible in lua? Because i don't know lua.