Is it possible to get end game achievements using save manipulations?
Solution 1:
It is certainly possible, I cheezed it the same way for the platinum. You can upload your save on your PS Plus account, make sure you deactivate auto-upload, then proceed to do as you suggested.
- Upload your save just before accessing the end-game area
- Get the first ending by choosing one of Gehrman's choices, download your save back on your PS4
- Get the second ending by choosing the other of Gehrman's choices, download your save back on your PS4
- Consume three umbilical cords, get the last ending, download your last save if you wish