The mods using the .xnb are the ones that overwrite your default game's files, full stop. The versions for the Content Patcher will tell your game to "ignore" the default one and use them instead. Usually when you go to the mods sites they do have the adopt'n skin listed on their requirements and you won't need json. You can have both a .xnb or a content patcher mod and the adopt'n skin version as they won't conflict.
All the default animals have a series of mods available to them, like Ellie's farm animals series, but I'm going to use my own mod as an example: I wanted beagles as my dog, so
I made it.
View attachment 11519
See? It has both the content patcher version that replaces the default dogs and the adopt'n skin version (in the optional files at the download tab)
To use the adopt'n skin version you download the file and place it inside your
Stardew Valley/mods/AdoptSkin folder
At the SMAPI prompt, write "
list_creatures dog " to find your dog's unique ID. Then write "s
et_skin skinnumber dogid" to change. If you want, for example a chicken, you would write "
list_creatures chicken" and then change your chicken, one by one. You'll know the skin number by looking at the .png name.
I know it looks complicated but it is easier when you actually try. And even if you do something wrong it won't be game-breaking, worst case scenario would be SMAPI changing the appearence of the wrong animal or being "sorry, idk what that command was, pls try again" so you don't need to worry about fiddling/trying