This guide will tell you in stages Mafia: Definitive Edition whether I can change the difficulty level to get an answer to the question - read on.
Yes you can. You don't have to stay at the difficulty level you chose at the start of the game. Depending on your preference, you can increase or decrease the difficulty, this also applies to the classic difficulty level.
You can change the difficulty level in the options menu. Go to the Game tab and find Difficulty.
Important note - one of the game trophies / achievements is associated with the classic difficulty level. If you want to get it, you cannot lower the difficulty level at any stage of the game. Otherwise, you will lose the chance to unlock this trophy.
And that's all there is to know about whether I can change the difficulty level to Mafia: Definitive Edition.