As Banjo said it is a grey area. His advice is sound.
If you like the convenience of self replacement and just thrive on DIY then knotted rope bridges are the way to go. Any 16 strand arborist line is a good choice since the load bearing part is the cover for easy inspection.
The problem with splicing bridges comes from the length. Unless you like a 36" bridge it takes a good bit of skill and knowledge to construct a short splice in appropriate materials. If you have the skill, rock on. If you want it, please practice, practice some more, get a bridge you spliced tested, practice some more, then go for it!
I have said this a thousand times already. If you like rope bridges, but are not replacing them with a regular, frequent program, then you are asking for trouble. Four or more rope bridges a year for a full time production climber is minimum in my mind, knotted or spliced.
Tony