Posted: 07/12/2014 at 14:05
Taking branches out completely will do no harm and as Gemma says - this is the time to do it. Trimming the green parts back into old brown wood is what does damage. If you wanted to 'trim' a conifer to maintain it's shape, you wouldn't cut farther back than that year's growth, and you would do that during summer/early autumn, which is not what you'd be doing John.
Unfortunately a tree that size pushes against (and often breaks) fences, which seems to be the problem you have there. I'd take as many branches off as you can - right back to the main trunk. I've been doing the same thing here with a mature conifer at the rear of my shed.