Hi Arthur
Tony's right, whilst the corms are small it's best to just put the whole rootball/potfull into new compost. I do this around about the time when the leaves are starting to die back, probably in August or even September sometimes. The thing about C pelistericus is that you have to bear in mind that it is not like most crocus. It absolutely must not be dried off. Like its near relative C scardicus, C pelistericus grows in bogs; the main area is Mount Voras (Kajmaktcalan) in northern Greece along the border with Macedonia. I think it is also found on Mt Gramos in Albania. On Voras it grows in huge numbers in wet peaty soil with sedges over metamorphic rock. See the Alpine Soc Bulletin for Sept 2000 (this also references an excellent earlier article with stunning photos by Alan Edwards).
Having said all this, I have grown and flowered seed collected from the MESE expedition and C pelistericus has proved to be a very amenable and quite adaptable plant, in all but the very dry parts of the UK such as where Tony lives. Unlike scardicus which I gather is altogether more difficult (I've had no success with germinating this let alone growing it!!!!). I use my normal bulb compost which is a 'good' JI compost with added 50% grit. To this I add some silica gel 'balls' to help retain moisture. Some growers stand the pot in a tray of water during the main growing season, but I have not found this necessary. I have also grown it in damper parts of the garden.
Good luck with it, this crocus is one of my absolute favourites - such a wonderful colour, well worth the effort.
Dave