It looks like you are referring to a NSP (Nintendo Submission Package) file for Fire Emblem: Three Houses, specifically an update file (version 1.2.0). Here is informative, factual context regarding this file and its contents.
A new "Everyone" option allows you to change the appearance of all characters simultaneously. Fire Emblem Three Houses -NSP--Update 1.2.0- -2...
If you have any questions or feedback about the update, you can contact Nintendo's customer support team or share your thoughts on social media using the hashtag #FireEmblemThreeHouses. It looks like you are referring to a
Beyond the flashy new content, Update 1.2.0 cleaned up the experience: Additional uniforms, stat boosters, and support items