Flourite to Aquasoil swap in a stocked tank?
Yes, aquasoil will release a lot of ammonia in it to the tank, and you need to do water change mostly everyday for a week to make it cycle again, even with a cycle filter. Then when you remove the flourite, there's a huge amount of NO3 will be released from underneath the substrate. The fish will get extremely shocked and stressed.
If you wanna swap, you should put your live stock to another tank until it's done and cycle!