[sblock=voda]ok... let's leave plot hooks coming to my mind that I can't tell you about now

...
Mechanically I'd say this is flavorful, and can work, but we have to balance advantages and disatvantges with those of an average warforged fighter. So let's say you have basically two choices (like the weapon mastery of fighters). you get +1 to-hit with your style of choice. That is permanent, but you can change the "conformation" at every extended rest (like a fighter could switch between having a shield and having a two-handed weapon) In both cases, your hands are not suitable fro weapon use and you receive no proficiency bonus from them. Also, if you use the first conformation, you can't use a shield. If you choose the second, your arm slot are considered occupied (as if you had a shield). You can't be disarmed. Here are the choices I thought about:
1- Both your fists become covere with rocky formations, and your knuckles ahow signs of crystallization. You can use your fists as +3/1d8 dmg+1 weapons. You benefit from feats and powers as if you were using two-handed weapons. (eg you can use potent challenge)
2-One of your fists is covered with rocky formations, you can use it as a +2/1d6 weapon. The other hand, along with the underarm, is hardened and becomes significantly larger. You don't gain an AC or reflex bonus from it, but you benefit from feats and powers as if you had equipped a shield (eg you can use tide of iron)
We can think about custom feats, magic items, or even paragon paths... tell me what you think about it.[/sblock]