It isn't hard to do so in python, most likely in C:\Program Files\Firaxis Games\Sid Meier's Civilization 4\Beyond the Sword\Mods\Fall from Heaven 2 030\Assets\python\CvEventManager.py (which is where the Infernal's unit spawning , treant spawning, Planar gate units spawning, Infernal and Mercurian entry to the world, etc., are handled)
I'd probably use "def onBuildingBuilt(self, argsList):", "def onCityDoTurn(self, argsList):", "def onImprovementDestroyed(self, argsList):", or "def onImprovementBuilt(self, argsList):" (I have already added several things to the first two of these)