No Append options

There is no option to append in the "Select action Type" dialog drop down menu, it starts with "Case conversion", I see no Append option there? :unsure:
Mp3tag v2.55a April 24, 2013

To append something to a given field, you could use a 'Format Value' action with the original field value repeated within the format string. As in this example:

Action type: Format value
Field: ALBUM
Format string: %album% (%year%)