Changing spark plugs at 30,000 miles?

After finding out that '07 and older GTs have a crappy spark plug that should be replaced before there's too much carbon build-up I'm concerned about replacing my plugs. I have about 29,000 miles on my GT and am worried that if I try to replace them there will already be too much carbon build-up and I'm going to break them off in the head.

The highest mileage I've read about someone replacing them was 17,XXX miles I think and they appeared to have no problem. If I use a lot of penetration lubricant and give it plenty of time to work should I be fine changing my plugs?

Also, how many people have actually had problems with the plugs breaking off in the head? I know this is a preventative maintenance thing so that the chances of it happening down the road are reduced, but has anyone actually had this problem on a Mustang GT?

The car is still under warranty. I'm thinking I may just leave it alone until I have to bring it in for some other repair and have them swap out the junk plugs for one piece plugs. If I let them do it I'll be sure to let them know of this issue and to be as careful as possible. I just don't want to do it myself then have one or more break off and have to tow it to a shop and decrease my chances of it being covered by the warranty or by Ford.