No. Before starting the story mode in Ace Combat 7, you choose one of three difficulty levels:
and is valid until the end of the whole campaign. They differ in the durability of our airplane against enemy fire and even the amount of points to gain in the time limit in several missions. Playing at the highest level is greatly facilitated by the planes and improvements available later in the campaign, so you can keep this mode for repeating missions or re-telling the story.
If you decide to stop the campaign and start again at a different level of difficulty, all credits, planes and unlocked upgrades are kept and go straight to the new game!