I got all the "one night stands" and chasing after a "good time" out of my system before I got married. Now that I'm happy and married with an amazing wife and child I can honsetly say I would look at the centerfold ... do the old "heh if I ment you back in my "play days what I would do" then walk away happy knowing I had my fun back in the day and now I have some one to share my life with not just my bed!
That I believe is one of the big problems of peopel getting married .... they don't take the time to get all the stupid shit our of there minds / systems before they get married then do a double take a couple years later going "shit I'm going to die before I do XYZ I allways wanted to". Then they do XYZ with the "maybe my wife/husband wont find out" ...but we all know how that goes!
Personal decision. For many of us, it doesn't matter if wifey finds out or not. YOU'LL know and that's enough of a deterrence. Unless you were part of a "shotgun" wedding, YOU are the one who vowed to be faithful, it's a matter of personal honor and integrity. Hopefully you've got a relationship that's honest (and fun) enough that you can share what happened with your spouse and she'll role play a centerfold for you ...
There is also the thing where, if you are going to cheat, the woman of your dreams wouldn't have a problem with it. The only problem with cheating is the risk of getting something you pass to your partner and your partner's opinion of cheating. If you find someone who is willing to be with you, but be polinamourous, the only think you have to worry about is your extra marital adventures are clean.
Cheating is only a problem if the person you are cheating on, believes it to be a problem. If the girl of your dreams is against cheating and you still want to cheat, go back to sleep and try again.
It's really easy to say "no" on a keyboard because that is the intelligent thing to do. However, it's quite a different situation in the moment to resist if this were actually to occur.
But what is the moment? Is it the Playboy centerfold girl running into you at the grocery store, and you stopping and asking if she'll go home with you? Or is it you bump into this girl and she says "hey, you're a guy, want to go home with me?"
I know if I was approached by an attractive man who said he wanted to sleep with me, I would be at least nervous or a bit shy in the first place (besides thinking why the heck is some hot guy approaching me randomly and offering me his peen?), and right there is where you would think "oh maybe my wife/husband wouldn't want me to do this."
It's not like you just happened to be at this woman's place against your will and your manly parts fell into her. There would still be a thought process behind it, whether you go through with it or not.