Ubisoft encrypts saves with your specific User ID. You cannot simply drop a new .sav file into the 720 folder. You must use a tool called AC Save Tool or Unity Save Editor.
You cannot hex edit on console. Instead, you need a Save Wizard for PS4 or a Horizon tool for Xbox 360/Xbox One. These are paid third-party applications that allow you to re-sign saves. Alternatively, use the built-in mission replay feature (explained below).
You’re asking about the save-game sequence for Sequence 4, Memory 1 in Assassin’s Creed Unity (the mission sometimes referred to in guides). Below is a concise, spoiler-aware walkthrough and tips for completing it and ensuring a clean save. assassin 39-s creed unity save game sequence 4 memory 1
Recon
Entry
Inside the compound
Objective execution
Exfiltration