I don't know if there is another way to load the mods without replacing the original files, but I recommend creating a backup of them :), just put the .bundle file in the following path:
SteamLibrary\steamapps\common\Rune Factory 5\Rune Factory 5_Data\StreamingAssets\aa\StandaloneWindows64\

Beatrice Bikini = Everyday Outfit
FemaleBikiniRF4 = Everyday Outfit
FemaleTopless = Swimsuit Outfit
FemaleUndies = Female Pajamas
FuukaBikini = Everyday Outfit
FuukaTopless = Swimsuit Outfit
LudmilaBikini = Everyday Outfit
LudmilaTopless = Swimsuit Outfit

Have Fun!

