Even if a modded app claims you have "Premium Unlocked," when the app asks the server for the video, the server will check your actual account status, find that you haven't paid, and deny the stream. You cannot patch a server-side check with a client-side modification.
Unlike a simple offline game, Netflix uses Widevine DRM (Digital Rights Management) and certificate pinning. The app does not simply check a local "isPremium: false" flag. Every stream request is authenticated against Netflix’s servers using your account credentials. netflix modded ipa