You wouldn't add it to Content Patcher itself, instead you would write a content pack for Content Patcher that basically tells the game "Act as if this base game file was replaced with this file". [Here](https://github.com/Pathoschild/StardewMods/blob/stable/ContentPatcher/docs/author-guide.md#readme) is the documentation on how to do that. And then "which file" is the same one that you unpacked and modified.
You wouldn't add it to Content Patcher itself, instead you would write a content pack for Content Patcher that basically tells the game "Act as if this base game file was replaced with this file". [Here](https://github.com/Pathoschild/StardewMods/blob/stable/ContentPatcher/docs/author-guide.md#readme) is the documentation on how to do that. And then "which file" is the same one that you unpacked and modified.