A* pathfinding for dynamic obstacles and player made blockages?

Hi I’m creating a TD in Unity 5 and need some help with my Pathfinding.

I’m going to use Arons A* pathfinding for my AI which enables me to use dynamic objects and update the path during runtime. However in my game I want the player to be able to block the minions with special turrets which will force the minions to attack the “block tower” instead to get past to their destination.

How could I accomplish something like this?

Image for more clarity:
alt text

private bool CanAttack = true;
void Update()
{
GameObject Obstacles = GameObject.FindGameObjectsWithTag(“SpecialTowerThingy”);
foreach (G in Obstacles)
{
if (Vector3.Distance(transform.position, G) <= DistanceToAttack&&CanAttack)
{
G.GetComponent().Damage(TheEnemysDamage);
CanAttack = false;
Invoke(“ToggleAttack”, YourAttackRate);
}
else
{
Path.destination = TheEndOfTheLevel;
}
}
}
private void ToggleAttack()
{
CanAttack = true;
}