Matt, it is a tough call. I have had single mouldy eggs be fine in a clutch and not affect te others around it. Then last season, I lost half of a clutch due to one egg down the bottom of the clutch. It turned only a few weeks before hatching due date. I left it as I thought it would be too hard to remove and as a result, it turned about 8 other eggs that were close to it. This was all in the last week or so, so very disheartening.
Siince then I made a decision to remove any egg that has turned no matter how hard as the risk of loosing more eggs to the one bad one is just not worth it IMO.
What I do is slowly and gently separate the eggs into individuals and then just throw the bad egg away. They will separate from each other, just do it very carefully and slowly and you should be fine. They are a lot hardier than they seem. Then you completely eliminate the risk of it affecting any of your good eggs. I have tried several methods of emptying the eggs contents, but have found that separation and getting rid of the whole bad egg as a complete item gives the best results. Of course opinions vary, but that is the way I go these days... GOOD LUCK!!
Zac.