The behaviours of the plugin are to:

• Re-type entire compound words.
  • In Epistory, backspace will remove an entire word, so compound words will not type correctly from Plover. By backspacing the whole word and re-typing it as part of Plover's output, this allows words of any length to be written in-game.

Epistory can be modded, and you can change both the controls, and the wordlist, see This guide on modding Epistory