This one can be extremely annoying, especially if you are in late game. So I found easy workaround.
- Make sure you are no longer gaining any prestige (sell everything if needed).
- Find your exact prestige level (mouseover "Legacy" tab, if your prestige is too high, turn short numbers off in options, so you can see the exact number and if you are in the middle of a run and you gained new prestige level, don't forget to add it to the final number).
- Close the game.
- Go to:
- Make a copy of "main.js" (just in case).
- Open "main.js" (notepad will do, but it's better if you have notepad++ or any other app that can properly read code).
- Search for "(Math.ceil(Game.prestige)%1000000==777777)" line and change those six sevens to your last six digits (for an example, if you have 1,787,221,117 total prestige, it will look like this "(Math.ceil(Game.prestige)%1000000==221117)").
- Ascend and you'll be able to buy those upgrades.