Well I wouldn't think that you'd have to do any fiddling just to swap the belts. And tbh I really can't see why you'd have to disconnect the battery. It's not a case of fitting megane belts and cutting and pasting and drilling etc, the yellow belts are clio belts anyway, just different color. It's only a case of swapping them I suppose?
Anyway, I asked Karl for prices, he needed a reg number from a clio that has yellow belts because the color wouldn't come up and apparently the fronts cost approximately £75 each but the rears are a bit more expensive (£150 each). So we are talking around £450 for the set...I'm waiting for mine to get a bit dirtier and I then I might go for it, tempted even though is an expensive aesthetic upgrade...