Don't know if you mean does it get changed if your windscreen needs replacing or if you just want to replace the cover itself?
If you just want to replace the cover, its pretty simple. Once you've taken off the wiper arms and the some seals under the bonnet, from memory it just pops out from some push in clips.
If your getting your windscreen replaced, I don't know if they would cover replacing it or not as its just a removable cover to get access to the lower part of the screen.