Will the already purchased tokens be adjusted to the price?
From the article about the change:
The new value of a GRAIN token is not just applicable from this day forward. It also applies to every contribution made by early investors, presale participants and current ICO contributors. So in the upcoming days, theyll receive double the amount of GRAIN tokens.
The Grain token sale dashboard will be updated to show the correct amount of tokens, and the additional GRAIN tokens will be distributed to the participants wallets.