In theory the answer is yes. However, this has to be tempered with the usual advice that you must always leave greenery on the branches as they will not regreen from bare branches. Also, cold frost laden winds can scorch the foliage. This is why winter pruning is often avoided. If you have trimmed the bushes hard and you have some really cold windy weather then this may cause damage or death. So, if you're not hard pruning your trees, or live in an area not prone to hard frost then you could probably get away with it, otherwise wait until the milder weather...but before the birds start nesting!!

It's also a good time to dig up Leylandii and put them on a bonfire!

Which is what I would do with Leylandii! But chaqu'un à son goût as they say here!