...and Gandalf suddenly had a brilliant idea of how to win the war.

[Kuruharan]

They would merely be making use of something that was already created. That is a major difference.

Not if they pull a Saruman and create a new strain.

At the risk of opening up the ole "what exactly are orcs" can o' worms, by breeding orcs and/or adding new DNA to the pool, one would be perpetuating and expanding upon the maiming of Life that Melkor engaged in.