How would I say "That had changed the game"?
Pluperfect: Das hatte das Spiel verändert.
Thanks, the umlaut threw me off.
I guess your English version is ambigous here. It could be past perfect or conditional. (if) that had changed the game.
In German it is cleary conditional II.
would this be correct: "That would changed the game."
you need the "have" for English grammar.
That would have changed the game.