Clearly the application is quite important. Without knowing more about it's potential use, it's hard to say if substituting dyneema/spectra is appropriate. Putting knots in dyneema/spectra significantly reduces the strength of the loop/cord, especially at the knot. The material is also static. No shock loading or it'll snap in a jiffy. Static loads are okay, and a triple fishermans knot might prevent the knot from slipping. Again, application.