Honestly, it wouldn't be hard at all. All you need is:
- A fairly large city on a river to house the queen, the guard, and the noble houses. Be sure to read modules 1, 2, 3, and 6 so you know what locations you'll need in your city. For example, in Module 3 you'll need an island in the river that can be isolated from the rest of the city. Or an old fortress within the city whose walls are still unbreached. Some way to isolate a decent-sized portion of the city to let anarchy reign within.
- An open expanse of arid wilderness. See the description of the Cinderlands in Module 4. This area should be at least a hundred miles across, so that the characters spend days traversing it.
- A mountainous region with an old haunted castle. See the description of Scarwall in Module 5.
The only reason I'd hesitate is that the Guide to Korvosa is so well-done; my players spent quite a few hours wandering Korvosa and meeting people described in the guide. I was able to add family members and friends that they had to get out as things got worse and worse.
On the other hand, you could just buy the guide and rename the city to whatever you wanted.
I've moved campaigns quite frequently as a GM; it's really not much trouble. Occasionally you'll be describing something to the PCs and there'll be an irritating location reference that you forgot to excise, but PCs are fairly forgiving of such little slips.
Good luck!