Thanks for the opinions. It does seem like some trails stay out of the firing range zone, but as I plan to hike the whole ridge to Tin Shui Wai, I think I have no choice but to go through it. I can deal with crappy trails but would prefer to avoid getting shot So best do it on a Sunday I guess.
@HK_Katherine: A couple of years ago I tried to go from the butterfly beach path and indeed, I couldn't find it! Actually, there was a massive construction site by the road and up the hill making it impossible for me to cross the highway in a place that would allow me to reach the trailhead (or at least where I thought the trailhead was). That was a while ago, so things may be better now, if anyone has any recent reports, it would be good to hear. Thanks for the tip about the Tin Shui Wai end - I'll be taking a headlight then in case I also can't find the exit and need to backtrack. I'd rather suffer extra hours of hiking than call helicopter rescue!