I downloaded and modified a style file and placed it in the Notepad++ themes folder. I was able to select it and have it update the style as expected. I then went to Setti
Setti
If you are on Windows 10 the path to add the new theme is :
C:\Users\NAME-OF-COMPUTER\AppData\Roaming\Notepad++\themes
stylers.xml is located one director/ folder above the themes :