Unfortunately you can't unlearn the guineas about thinking they are the same as the chickens. The best solution if you really want to keep guineas without them terrorizing your chickens is to start over without raising the guineas with chickens. Give them their own area and have enough of them (minimum of 10) that they can satisfy their flock needs.
And I suppose the next generation of guineas, even though they were raised by a guinea and don't think they are the same as chickens, still learns to pick on chickens. Sigh.
Seriously, these gangsters and their attitudes are making ducks and their slobbish obsession with water and all things mucky look like an easy problem to solve.