Torquing the bolt head can produce a different torque value than it would at the nut. This depends on the surface area of the bolt and nut, the coating of the nut/bolt, and the material of each side being clamped.
The whole point of torque specifications is to produce a semi repeatable clamp load. This clamp load is essentially directly proportional to the torque, however friction is involved. This is the friction between threads, friction between the bolt head or nut turning on the surface of the part. Some hardware comes with wax, zink, light oil. All of these help to lower the coefficient of friction to make a more consistent torque. So with this, when you add anti seize, loctite, grease or anything it will effect the torque. If the manufacture specs it as a dry torque then adding anti seize will probably over torque it slightly.
At the end of the day, just need to make our best informed decision to decide if torquing the bolt head is ok and adding never sieze is good or bad. I've personally done both in situations like this and wouldn't worry about it.
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