After completing the Operation Anchorage equip the Chinese Stealth Armor.

Then wear as many beneficial hats as you want.

The DR, S.P.E.C.I.A.L. and skill increases will stack and stick even after removing the stealth suit.

Unfortunately you cannot wear two of the same headwear and the weight can get up there.

This does not work for glasses or mask s(AntAgonizer's Helmet works).

It works with Power Helmets as long as they are different types (Tesla, Power, Outcast, Brotherhood, Winterized, etc.).