Personally, I would allow the berries to ripen and leave them for the birds to feed on, then cut back to the desired height etc, when there is no signs of frost around. Good Luck Tbird+
We cut ours back in winter after the birds have stripped the berries and before the young shoots start sprouting in early spring.
This is such a hardy shrub that whatever you do to it at any time of year, it seems to recover. We even cut one bush right back to the roots and two years later it is back in full growth again..