Change the .ext file extension to .zip and unzip the files. If you do this to a directory within the \extensions folder you can edit the files directly and when you reload Fantasy Grounds (stop/start FG or type /reload in the chat window) it will load up your changes.
Some info on modifying the ruleset here: https://www.fantasygrounds.com/forum...oreRPG-ruleset A lot of it is relevant to modifying an extensions (basically editing the .ext extension file rather than the .pak ruleset file).