Theoretical security of mining bitcoins Is it possible to change rules of mining bitcoin division?


rewrite P2P bitcoin client (or write maleware) which will be pretending that fake bitcoin client is legal, original client 
distribute program more/less widely
then by fake client division of mining loot will be with fake/own rules (e.g. give more bitcoins to farm X, even if farm X didn't work more than others)





no changing keys
no faking difficulty level/spent time
maybe changing proof-of-work action
Yes, it is possible.
This is "hard-fork" (bitcoin with other rules) or "alt-coin" (any crypto-currency with its own rules)