unbroke, I don't know what will happen, but here's what Felpro says could happen with their gaskets -
NO CHEMICALS, PLEASE!
Under no circumstances should any type of chemical sealer be applied to a soft faced, coated head gasket. This includes adhesives, shellac, tacky sealers and RTV silicone.
If a chemical sealer of some type is used on a coated gasket, it may react chemically with the coating material. This, in turn, may prevent the gasket from cold sealing properly -- or worse yet, it may cause the gasket to deteriorate and fail.
A sealer may also undermine the anti-friction characteristics of the surface coating, causing it to stick when it shouldn't. This would increase the shearing forces on the gasket which could also lead to failure.
If RTV silicone is applied to a head gasket, it may flow when the head is clamped down and enter the combustion chamber and/or cooling jackets. What's more, RTV silicone is not resistant to gasoline and would quickly dissolve leaving gaps that could become leaks.
The added thickness of a heavily applied sealer on a head gasket could also cause uneven loading and loss of torque retention which could also create leaks or cause the head to warp.
