全員この場で野々村の宣戦布告を受け取る。
We all accept Nonomura's declaration of war.
たとえ遊びでも手は抜かない。
Even if it's just for fun, we will go all out.
How would these lines have read differently if it said たとえ遊びでも手を抜かない. I understand that when は is used to replace を it is essentially はを but how does using は instead of を change the meaning of this sentence?