When .plist file is manually updated on MacOS 10.9+, changes are not directly applied to plist cache. This means that these changes aren’t visible to executed application (even if you run it after plist change).
It’s necessary to tell plist change to reload this settings. There are two ways how to do it. First one is simpler but doesn’t work if you completely remove .plist file:
defaults read ~/Library/Preferences/com.xxx.xxx.xxx
Second method is much more efficient, but requires to completely kill plist cache. This cache is immediately executed again and during this launch all plist files are scanned and loaded again: