Desalinating dried/smoked fish
You are correct in that salt fish are very salty. Where we live salt herrings are a tradition. The way to remove the saltiness is to soak them, changing the water every few hours.

The trick here to really getting the saltiness out is to split the back. (The belly should already be split.) This is really important. 

I once had someone cook them for my family and they were so salty you could barely stand to eat them. When asked if they had soaked the fish they replied that they had soaked them for two days! Then someone asked if they had split the back and, of course, the answer was no. They didn't know to do that. 

If soaked properly the fish should not be totally fresh but should taste like fresh fish that you seasoned with salt.