Interesting concept. Though the way you describe the Nekoken and people
knowing about it are very rare. First the Nekoken is extremely rare and many
do not know about it or in the middle of a conversation say oh hey, the
nekoken is learned this way. If a Master does know about it, he may not know
the techniques and if he does he would never tell someone about it. It is
not a useful technique and a martial artist or ninja 99.99% never meet a
practioner of the art and if they did he had to be crazy to use tits full
powers.
Second the instruction never said anything about "or like substances." Genma
was stupid enough to try other food product when the fish sausage did not
work.