The rule for antiseize or oil of any kind on a fastener is its OK to put it on the threads but not under the head. The head is where most of the friction occurs upon tightening. As long as you keep it off of the head area then it shouldn't affect the torque too much. There might be a spec somewhere. I would not reduce much on a spark plug. The consequences of it loosening are too serious.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra