All of the values in the JSON column will be transformed to a JSON array with " JSON key " key complemented by the custom key/value pairs, or just the array if the option Omit root is selected. (The JSON content in the file can be pretty-printed.) The output looks like this:

{
  "JSON key": [
    {"json":"from Row1"},
    {"json":"from Row2"}
  ],
  "custom key":"custom value"
}

where the JSON key can be specified with the Add root object with key parameter, the "custom key":"custom value" is specified by the Custom key/value pairs and the Collect into array options.