A lot is written on the knot subject. Knots are usually created for specific purposes.
Fishing knots- are usually tested on weirdly, fishing line. This is predominantly a monofilament or a small diameter woven line.
Sailing knots-these are of some use. A monkeys fist is particularly useful for making sure people don't do the same thing again. And we get the bowline from it. A knot that regardless of how tight it gets can always be released. There are variations on how much strength you lose, but lets say 50% ish
Climbing knots- there are lots of good ones. The modern rope that climbers and yachting people use is more of a rope system. The inner is a high strength fiber usually linear covered with a protective woven exterior. The interior slides inside the exterior sheath. Not much, but enough to make a difference on whether a knot bites or slips open.
So we've established that the general testing results will be similar but not the same as the cord, woven flat or small diameter that we use in rocketry.
What do I use?
If your cord is suitable, the fingertrap method works well. But it does require to be implemented over a good length. If I had a 100 lb rocket, I'd be using rope of a large enough dia to be able to do that. The tubular kevlar is big enough but 2000lb Emma kites kevlar is barely big enough to do that. I have no idea why you would need 2000lb kevlar on a 7lb rocket. Are you planning to tow some people out at Black rock?
If you terminate to a small dia welded ring like the ones that are fitted to the large ball bearing fishing swivels, I'd put heatshrink on the cord, wrap twice through the loop and secure back with a few half hitches . Pull the tail back trough the heatshrink. Push heatshrink up covering half hitches and some/all of tail and shrink the heatshrink.
Or use a bowline with a half hitch and HS over the knot/tail and live with the strength reduction.
The knot police will arrive shortly......
Removing cord shock is much more important than increasing the strength of your cord. A single 700 lb cord would be more than enough strength wise but might not provide enough physical protection from rubbing at the body tube contact point or others. Although kevlar is strong, there's not a lot of it needed for that strength so losing small amounts from chafing can result in significant strength reduction.
.Good luck with the flight.