Posted: 12/01/2016 at 10:58
I have never had any success with cuttings - and I've tried in all seasons.
I have just lifted eight of my clematis and planted in deep pots, different varieties, as part of the garden is about to be bulldozed. Three of them came up with additional plants attached and all have made many new growths due to the warmer winter. The only one that worries me is a very rampant Armandii and now is absolutely the wrong time to be lifting it - but needs must. This was the only one with the equivalent of tap roots, and these had to be severed - so fingers crossed on that one but it is residing in copious quantities of lovely home-made compost.
I can't see that splitting as you suggest would do any harm at all, so long as you protect the roots well with lots of compost afterwards.