Welcome to Librarium Online!
I know that with Nobles and Highborns of the Eternal Kindred use the Eternal Guard Fighting Style special rule, and lose it if they take any magic weapons or armour, but if you were to equip them with something like a great weapon, would they gain the abilities of the great weapon, along with the effects of the Eternal Guard Fighting Style, or would the Noble just get the effect of the Fighting Style?
David has said it all.
Fighting style overrides weaopns.
"Ask not the Eldar a question, for they will give you three answers; all of which are true and terrifying to know"