This weekend I replaced the spark plugs on my sister's 2008 Expedition with the 5.4L engine. Hers is an early 2008 so it had the black boots and the "bad" spark plug setup. It also has 118K miles on the original plugs. Yikes. After seeing it mentioned on here in a few threads and after watching this video:
I decided to go with the impact method. It's not explained anywhere that I can find, but I kinda figured out that the reason this works is it does not give the seized plug time to get hot and expand in the head. You kinda sling the carbon off the plug and it's out before it can get stuck.
I did have her run a can of Seafoam in each tank for 3 tanks beforehand and I brought it into the shop hot, just like the video says to do. I went 7 for 8 and only broke 1. It was the second plug so I had to nut up and continue but got the other 6 out with no problem. The Lisle extraction tool worked perfectly and the stuck plug remnant came out fine.
I used a 1/2" impact on the front 3 plugs but I had to use a smaller 3/8" impact on the back plugs. On those I broke them loose first with a ratchet since the little impact isn't nearly as strong as the big one.
I used NAPA Nickel Anti-Seize and torqued the new Motorcraft plugs to 25 ft-lbs.
I recommend this method. It worked for me. I did break the one plug, but with such high mileage on the original plugs, I was pretty happy with that outcome.