Bullying terms in Kipling's "Stalky and Co." (contains spoilers)

Solution 1:

Are these made up for the purpose of the story or are each these idioms/phrases previously established?

They were likely established before Kipling's use.

Actually, Kipling regularly took offence at the implication that he drew from an imaginary lexicon, rather than his world experiences.

Vast amounts of these words were documented, as described in this book on slang which gives many examples, but unfortunately much has not made it from manuscript to internet.

Solution 2:

"head knuckling" was in use when I was at school (1970's) in Dublin, Ireland. It meant literally that: A boy, holding another boy in "head lock", dragging his clenchfisted knuckles (perhaps "knuckles of his clenched fist"?) backward and forward on another boy's scalp. Most painful in my memory!