Add a filter or a translator. One of the arguments to that filter is
the plist you are looking for. Work back from there and you will get
the right APIs to use.
The snippet below from ox-odt.el should be a good starting point for
further exploration. The translators do fairly *non-trivial*
transformation on the "lispy" parse-tree before triggering off the
actual export. There you will see the APIs for element translation.
:filters-alist '((:filter-parse-tree
. (org-odt--translate-latex-fragments
org-odt--translate-description-lists ; Dummy symbol
org-odt--translate-list-tables)))
