There is a way to change NC to dark in macOS Sierra without replacing system files (it may be glitchy).
You need to have SIP disabled
Then, you need to download mySIMBL from GitHub: https://github.com/w0lfschild/mySIMBL/releases
After opening it, you will be prompted to install SIMBL. Install it.
Then go to "Discover" and click on "Wolf's plugins".
In there, find darkNC and install it.
After installing, restart NC (or log off and log on back).
And you're done.
(And maybe it'll work in macOS High Sierra too)
[doublepost=1515928561][/doublepost]And with mySIMBL, you can enable dark theme in other apps like Finder or System Preferences.
You need to have SIP disabled
Then, you need to download mySIMBL from GitHub: https://github.com/w0lfschild/mySIMBL/releases
After opening it, you will be prompted to install SIMBL. Install it.
Then go to "Discover" and click on "Wolf's plugins".
In there, find darkNC and install it.
After installing, restart NC (or log off and log on back).
And you're done.
(And maybe it'll work in macOS High Sierra too)
[doublepost=1515928561][/doublepost]And with mySIMBL, you can enable dark theme in other apps like Finder or System Preferences.