- Don't use _label -- whatever_label is only for labeling whatever. (This is probably your problem.)
- Make sure you have a space leading each line to be included in multi-line config items such as custom_columns_settings.
- Put it in the correct section -- putting it in [overrides] will effectively disable custom_columns_settings in any other section.
- Use add_to_ feature in case you want to put other, more common metadata entries in [defaults].
Code:
[www.fimfiction.net]
add_to_custom_columns_settings:
likes=>#likes
groups=>#groups