I wouldn’t call it a “trick”, it’s just disconnecting from the internet. You don’t even have to physically remove anything. Just go into options on your console and disconnect from internet. Go back into the game as it will prompt you to either go to menu or retry connection. Just go to menu and then reconnect to internet, then log back in to connect to the hitman servers.
People that do it and have a failed target must be doing something wrong becuse the game is already programmed to not fail you if you lose connection even after completing an objective. This was implemented when the season one servers were so bad and ppl lost connection after an objective was completed and that would instantly remove you from the server and give no ability to reconnect. Insta-main menu and fail.
But if one is not trusting of this method then ya, just use alt accounts.