If you are considering changing your windows, then you should absolutely replace them first before you install shutters. In order to make sure that shutters are fitted correctly, they need only be measured to the specific window and fitted once.
There is no doubt that the dimensions of the new windows will differ from the old windows, no matter how close they are, which will mean the shutters will not align correctly or might not be able to fit at all.
You also run the risk of causing damage to the frames when you remove them.
However, we do offer a service whereby we remove shutters (for decoration) and replace them when ready for a set fee.