If you prune now it will be at the expense of flower next year, but it shouldn't harm the plant in any way if you want to do it now.

Type this in the search bar and you'll find some posts on this subject. Some people prune in spring after the flowers have faded but that means you won't get any berries for the birds. At the garden centre I was told that if I pruned the tree in late winter I should still get flowers and berries next year. In fact they said that if it got out of hand I could cut it almost to ground level in winter and it would soon grow again!