vanquish help!

Hi guys really need your help, playing vanquish on hard difficulty setting, i swtiched it to easy during act 3 mission 5 because i wanted to go back and get the failure breeds success achievement. i noticed the message:

'changing difficulty mid game will default all leaderboards data and achievements to the lowest difficulty setting played'

does that mean i have to play the game from the start? or act from the start or the mission from the start? to get the achievements for completeing each act on hard or above.

please i need your help because it would such to start all over again

thanks

CAN SOMEONE PLEASE HELP

No...you'll play at the same level...just this game will be more easy..this time you got assist aim target...actually i'd play normal mode..it's very hard to win agains boss...