Crikey... you have to much spare time on your hands. But sounds awesome! Wouldn't recommend diving with crocs, but you do you. Also what does teaching crocs no to eat toads do if you are trying to get them to not eat fish?
Well depending on specie diving with captive Niles croc is dangerous to a degree but not suicidal like diving with Saltie. Diving with captive tame Gharial is safe though Tomistoma is also relatively safe to dive with if they are habituated to people.
I say i wouldn't use such method but using the same logic if i gave it a bichir injected with small amount of poison the croc would learn (erroneously) that bichir is poisonous.