Command-line ID3 tag editor that handles all tags

The mutagen Python module comes with a mid3v2 command.

mid3v2 --artist "Sigur Rós" *.mp3

Before you ask: No, mutagen does not support ID3v1, because there is no valid reason to be using it these days.

Just use Homebrew:

brew install id3lib

Example command: ide3tag

Usage: id3tag [OPTIONS]... [FILES]...
   -h         --help            Print help and exit
   -V         --version         Print version and exit
   -1         --v1tag           Render only the id3v1 tag (default=off)
   -2         --v2tag           Render only the id3v2 tag (default=off)
   -aSTRING   --artist=STRING   Set the artist information
   -ASTRING   --album=STRING    Set the album title information
   -sSTRING   --song=STRING     Set the title information
   -cSTRING   --comment=STRING  Set the comment information
   -CSTRING   --desc=STRING     Set the comment description
   -ySTRING   --year=STRING     Set the year
   -tSTRING   --track=STRING    Set the track number
   -TSTRING   --total=STRING    Set the total number of tracks
   -gSHORT    --genre=SHORT     Set the genre
   -w         --warning         Turn on warnings (for debugging) (default=off)
   -n         --notice          Turn on notices (for debugging) (default=off)

Source: https://apple.stackexchange.com/a/16145/53242

ID3 Editor
Although the linked website page is oriented towards GUI, it does contain "NEW! Command line editor".

Tagr was recommended; it's free, looks powerful (batch process, cover work, etc.), but not sure it has CLI.