Your better off just getting some cheap copper ones as the iridium ones never seem to last as long as they say they do. I have used them before and they have been rooted after only 10- 20,000kms so i doubt very much you could get them to last the supposed 100,000k's they say they are suppose to. The ones i was getting ere gapped to 0.9 and i couldn't re-gap them as Duncan said it damages or destroys the iridium coating on the plug. For a lot of money its just not worth getting the iridiums in my opinion.
Just get the cheap copper ones and change them every 5000 when you give her a service. I have done this with all 3 of my skylines and never had any problems with the threads in the head. Just dont over tighten it and to get them in out you will just need a deep socket the right size of the spark plug.
Easy as.