I think the best solution would be to gradually sand down the grip area rather than the hand, since the soft plastic and the round, unobstructed cannon is easier to work with.
Also, damage to this accessory may be easier to replace years from now, like with G1 toys, compared to trying to find an undamaged hand.
Then the cannon sword wouldn't look right - needed the specific grip area to emulate a tank cannon AND the sword, which means it needed an open hand. Problem was, they sculpted the hand a little too tightly, and decided to put the hand on the same sprue as the other orange plastic.