The administrator requirement was added in a patch for compatibility reasons for those who have NWN installed in program files. I personally find the prompt annoying, more so as I don't require administrator privileges as I have the game installed elsewhere.
I've modified the manifest file of my exe to invoke the exe 'asInvoker' instead of 'requireAdministrator'. No more annoying UAC prompts and the game runs with standard user privileges.
Something like Resource Tuner, Resource Hacker, or mt.exe (from MS Visual Studio) should be able to do it.