I suspect it is hard because after a resent post I cant find asked to changes the counties because what PGC uses as counties is not what someone living in the UK consider a county. Look at some map like mapcompare or map counties.
for example Leicester is not in the county of Leicestershire but a separate within.
If the counties that PGC uses is what the CO mean it it quite easy to create a checker or write a script if necessary.
If you have to combine caches in for example Leicester and Leicestershire. A script probably has to be written.
If the counties are incorrect polygons has to be created an a script written. I have no idea if the code to check that the caches is inside a county is fast enough. There are caches in the UK with then of thousand of finds
