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
If files are going to APPDATA, then you can create a folder called "themes" and then inside that place your new xml themes. Then close and reopen notepad++ and you should see your new style in the "Select theme:" drop down. Whatever you named the file should be what appears in the dropdown