As part of the collision definition that destroys the enemy sprite you can tell it to also activate a function. Then you can make that function create a sprite that looks like you want a dying/dead enemy to appear. The function should create the sprite relative to the trigger point, which will cause it to be created where the collision occurred.
And to change the tank when it's shooting you could create a sprite that ovelaps the tank to make it look different when it's shooting, but getting it to be in the right state might be tricky if it needs to point in a particular direction -- that might require script.
Does that get you anywhere?
