No, there is no way to change the damage.
Even if you catch the damage event and stop it from reaching the client, the damage is still dealt. We've been through all this before.
You COULD catch the damage event and give health back to the player, but that won't help in the case of AWPs, because the damage is dealt before the plugin can do anything...so if it would have normally been a one-hit kill, it still will.
Although...since the HUD looks the same at 100 and 356...you COULD give the player 356 health, and then if they go under 256 (AFTER giving the health back), you'd slay them...