When I was younger I made a zip-cord trolly from a big tree in my parents house to a smaller tree. We started at 20ft and went down to 2ft above the ground using 2 pulleys and a black concrete mixer (that looked like a boat to us![and we used it for that too!]).

Anyway, we used 130lb 'white' nylon cord from wal-mart. Looking back the rope was only rated at ~150lbs and two of us weighned in at probably 200lbs (total), add 15lbs for the tub and a couple for the pulleys and secure ropes we were WELL over our limit. We went down togther many times and the neighbors all had a go etc.. etc.. It finally broke one day from about 10ft we went tumbling through the branches and landed in the tub on the ground. The worst injury was a bruise form the pulleys hitting us on the way down.

While the paracord is only rated at 550lb if I was stuck on a rock ledge and had to lower some gear or myself down and it was my only option I think I would do it. Double it up if possible but if it was a matter of starving to death or using my paracord I don't think i'd hesitate. 140lbs of me x2 is only slightly more than 1/2 the paracords rating so I think there is plenty if safety margin for an emergency.