I don't see how that would help anything. As long as the knot is "in position" when it comes under tension it will tighten up correctly. I doubt it will be able to move after the first launch, if it even can now. The main thing is that the knot wasn't too close to the end of the cord. I might consider some protective tubing around it near the motor mount. Don't glue it to the cord though, most adhesives will weaken it.
Oh, and big heavy eyebolts are usually only used in high power, where more weight is a feature, use a bigger motor. Where I've thoughts eyes are better, I've fabricated them from clothes hangers and paper clips, lighter and maybe stronger than a nonwelded eye due to methods of epoxy or soldering them closed.
