You can edit with any editor that does not mess up the file.
Most Linux text files use a different end-of-line sequence than most Microsoft Windows text files, and many word processing type editors on all platforms have a tendency to “correct” assumed problems without asking.
Therefore, using editors that herald from Unix/Linux or are Linux-aware is safest when editing Raspberry Pi files. I trust editors like Emacs, VI, Vim, Nano, and Atom not to mess with the file. You can use Notepad++ but there are some situations that confuse it, and I am no longer current on using Windows in a mixed platform environment (retired three years ago).
First, you should only add this if you see an ipv6 networking problem, so not needed yet!
Second, no comma, and no blank line before or after are needed.
(If you are seeing the file as one long line, you need to be editing with a different editor!)
Third, you wrote the line with spaces around the equals-sign - pay attention to spaces because sometimes spaces are mandatory, sometimes they are forbidden, and sometimes they are optional - I looked at my file and there are no spaces, so I would not add them.