Open Player.java and search for:
playerEquipment[playerHat] = -1;
playerEquipment[playerCape] = -1;
playerEquipment[playerAmulet] = -1;
playerEquipment[playerChest] = -1;
playerEquipment[playerShield] = -1;
playerEquipment[playerLegs] = -1;
playerEquipment[playerHands] = -1;
playerEquipment[playerFeet] = -1;
playerEquipment[playerRing] = -1;
playerEquipment[playerArrows] = -1;
playerEquipment[playerWeapon] = -1;
Change the "-1" to the item ID of whatever you want them to be wearing. I'm not much on PI, but thats my best guess. If it doesnt work let me know.