A specific actorDo you want it to be a specific actor every time or whoever is occupying a particular party slot when the battle happens?
var actor = $gameActors.actor(your actor ID here);
var stats = [actor.hp, actor.mp, actor.atk, actor.def, actor.mdf, actor.agi, actor.luk];
$dataEnemies[ID of your party member monster].params = stats;
var actor = $gameActors.actor(22);
var stats = [actor.hp, actor.mp, actor.atk, actor.def, actor.mdf, actor.agi, actor.luk];
$dataEnemies[18].params = stats;