From what I gathered, the original thread was talking about ArtMoney. The idea was to modify the users' health and mana level and leave it fixed at a certain level. However, that information is stored on the server end and wouldn't work. That is, unless, you you owned the private server.
What makes me highly suspicious is that the God Mode movie shows _everyone_ in IronForge flagged for PvP. I've never seen that happen before. Usually, it's full of noobs or mid-levels that are never flagged.
If if is real, you would have to find some kind of exploit for the real Warcraft server that fixes your health/mana or makes you evade all attacks. In some cases, how an NPC is positioned (ie, on an incline), they can evade all attacks.
This bug has happened before apparently on the real WoW server and the character is vulnerable to AOE attacks. Just not direct attacks (of which they evade.)
If there is a way to do it, I suspect a macro that quickly changes inventory, spams spells, or requires the assistance of others (MindControl). For example, that dual-shield trick for a Shaman. What would happen if you created a macro that quickly equipped/unequipped trinkets/rings/weapons/shields/etc?
I'll do some playing around, and see what happens.