It does not work for me. I have EliBook (v5.4.10) core and below WindowSkin (v5.1.0) in the list of plugins. The console shows this. 
Demonyaka
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A member registered Aug 09, 2023
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Hakuen Studio Window Skin Manager for RPG Maker MV MZ comments · Posted in Hakuen Studio Window Skin Manager for RPG Maker MV MZ comments