I think a YAML file is reasonable, but not in user-editable contexts.
- putting YAML in a syspref, but not modifying it directly, but through a user friendly form on a specific page. I have never seen that in Koha, so I don't know if it will complies to the coding rules..
This is how "Did you mean?" is configured. There wasn't enough configuration required to justify a new table, so I just stuck JSON into the syspref.