Actually I did not know the answer to that one either, so I made a call just now and found out that this is an old "Wives / Shade Tree Mechanic's Tail" There is actually nothing wrong with changing either way, Amsoil Full Synthetic Fluids are fully compatible with all other oils, period.
I am sure someone will come in to argue that point, but I just double checked with Amsoil and that is per their information after 35 years in the Synthetic Lubrication Industry