Schinderdiv said:You can do the save manipulation when you get to the second drinking game (stacking) versus satan, saving you about 30 minutes if you're going for all endings at once. Unfortunately I didn't discover this until I had only the third ending achievement to go, but I tested it several times before finishing the third ending achievement and after getting the achievement (which is when the next autosave triggers) and it worked every time. When satan invites you to start the drinking game, the game autosaves, and you can do the save manipulation from this point instead (right before you get the option to "sit"). Perhaps I've overlooked something, but since all ending achievements seem to be related to the second drinking game (stacking) only, I don't see a reason to do it the long way.
Since I already got two of the ending achievements I can't say with 100% confidence this is guaranteed, but it seems like it should work from the tests I ran. I did use the method to see a different ending (beat satan), so logically, to me, that should trigger the corresponding achievement.
I never risked doing the checkpoint this late, but your reasoning is sound. To be candid I'm overly cautious, and categorically knew that outside Satan's would work. If I can replicate, I'll make the change (probably later this week). Thanks for your input!