I wouldn't be surprised if many of the "techniques" softened it but made it more resistant to shattering.

An extremely hard but brittle conker would probably make for poor results.

Interesting. I can certainly see how brittleness is probably fatal. But a soft one won't be any help at breaking your opponent's conker, either, right? Unless speed of your conker can overcome the increased inefficiency of transmitting energy into the opponent's...

Everything can be a sport if you try hard enough.

Everything can be a sport if you can bet on it.