Add a check within here to see if the projectile hits a brick, and the brick has that specific name. Nvm did it for you, this goes in Weapon_Hookshot.cs, replacing the function on line 280.. (btw this is untested.)
function hookshotProjectile::onCollision(%this,%obj,%col,%fade,%pos,%normal) 
{
	%player = %obj.client.player;
	%pmount = %player.getObjectMount();
	if (%col.getName() $= "_hookbrick")
	{
		if(isObject(%pmount))
		{
			if(%pmount.getClassName() $= "WheeledVehicle" || %pmount.getClassName() $= "AIplayer")
			{
				if(%col.getClassName() $= "Player" || %col.getClassName() $= "WheeledVehicle" || %col.getClassName() $= "FlyingVehicle" ||  %col.getClassName() $= "AIplayer")
				{
					pushPlayerToObj2(%pmount, %col);
				}
				else
				{
					pushPlayerToObj(%ppmount, %pos);
				}
				return;
			}
		}
	}
}