OK, this is going to be a bit long winded, mostly because I am bored and not much is happening here right now.

With cordage they tell you its breaking strength. From there you start applying your safety factors.
Safety factors are simply how much stronger you need to make things for safety, they are not like gambling odds where you say it might break one out of so many times.

A safety factor of one is no safety factor at all.

If your cord says it is good for 550 lbs them a safety factor of two says only try 275 lbs.
As the cord degrades from use you might want to increase the safety factor. If what you are doing with it is more critical you increase the safety factor again.

Scaffolders built scaffold with a safety factor of 4, so everything is built at least 4 times as strong as it needs to be according to the ultimate material strengths.

Safety rigging where MY life might depend on it gets a safety factor of 10.
( ie. Massive overbuild)

So if the cord is a bit shabby, factor 2, if it matters add that, maybe not so important if it fails, so safety factor 3, jerky load, safety factor 5.
So your paracord might be trustworthy for a 110 pound load under those conditions.
If you figure a safety factor of ten because what you want it to hold matters more to you, then you are saying you trust holding 55lbs on a brand new piece of 550lbs line.

(Usually safety factor 4 is good.)

Shock loading?
You need to calculate how hard you are hitting the end of the line.
You need to understand that the Kinetic energy of a moving load can be very high and increases at the square of the speed, but only directly with the weight.
The equation, if you want it is 1/2(Mass* Velocity^2)
So the weight times the square of the speed and then divide by 2 to get how much energy needs to be absorbed when it hits the end of the rope.
The way to balance Kinetic Energy is through Force times Distance. (fp Foot Pounds energy, foot pounds torque is a different measure)
In other words; shock absorbers.

Nylon is stretchy (10% strain is normal) so it actually absorbs shock loads pretty well, but it needs to have enough length of nylon to stretch and absorb the shock.
I have seen bungee cords used as shock absorbers (think of bungee jumpers).
Climber's safety harnesses sometimes use shock absorbing links that are flat webbing folded over itself and sewn with stitches meant to tear out. It is meant to reduce the shock loads to the point a human body can withstand them.
In the pictures in this link http://www.safetysupplies.co.uk/trolleyed/21/ you can see the shock absorber in the fall arrest lanyards. It is the white block on the yellow webbing, notice it is missing from the restraint harnesses. (screamer is the slang term for the shock absorbing lanyard, the fall that stretches it and the the person that ends up dangling from it. You have about 15 minutes to get him down after he stretches his harness. After 20 minutes he might be dead from compartment syndrome.)

Oh yes, all load ratings are for new material so keep that in mind.

Then come all the rigging points, knot weaknesses and angular loads.
It can get pretty complicated if you are not careful so with rigging KISS is important.

Safety factor 2,000?

(fishing line is different. because competition test weight ratings means it is guaranteed to break at the stated test weight instead of carrying at least that weight when new.
Eight pound test fish line is supposed to break before it has eight pounds of load on it.)

Edit:
Note what paracord was designed for. You don't get much more bounce than a parachute opening with a fully equipped footsoldier hanging below it.