To install:
1. Locate your Midnight Suns installation folder. In the Steam version, this can be done by right clicking on the game in your library and selecting Manage->Browse Local Files
2. Move the file called pakchunk98-feline_P.pak to the \Marvel's Midnight Suns\MidnightSuns\Content\Paks\ folder

This should work with existing save files. Some of the unlockable hunter suits still display with human skin, though I should be able update those in future versions of the mod.

The game sometimes crashes during loading due to low memory, so if that happens when using this mod, you might try closing all other open applications or restarting your computer.