Scotty86 is pretty much spot-on about this issue---it is largely overblown and Ford criticized for this but with the millions of plug holes that DON'T blow out it's somewhat rare. For the most part the brand Time-Sert is highly, highly recommended for thread repair. There are many other brands but almost everyone who has used those correctly the repair is permanent. However if your engine has no issues at the moment there's no real need go through all the trouble to remove the heads for preventative thread repair. Like Scotty though that'll have be to your call in the end.
On the issue of removal and
reinstalling plugs here's my recommendation..........
(Your engine should be the "older" style heads with 3.5 threads in the plug hole---this is incorrectly said to be the root cause of ejected spark plugs---its not.)
Before we get too deep into this its better to change plugs at 50K miles despite the idea they're still effective at 100K and above.
Use nothing but Motorcraft plugs spec'd for your year & engine. There is no advantage to using some whizz-bang gee whiz new-fangled overly hyped brand. They're designed and built to work on Ford engines, the PCM seems to love 'em and what's better than a trouble-free install?
There is too much anecdotal info where a misfire with new plugs is related to another brand. Just as often these misfires are corrected by installing a Motorcraft plug.
Removal of the plugs especially after 50K miles can greatly affect the re-installation and longevity of plugs in the heads. There are recommended procedures IF issues with removal are encountered. Because this is almost as important as installation it pays to know what works best.
During installation I highly, highly recommend using a nickel-based anti-seize on the plug threads, torque set to 23-25 ft/lbs. (These heads have been tested in a casual manner by an FTE user in excess of 90 ft/lbs without any signs of stripped out plug holes. https://www.ford-trucks.com/forums/1...ead-heads.html
I've used the anti-seize and 23 ft/lbs technique over several 5.4 Modular Motors, some with much higher mileage than yours. Being careful costs nothing and can very well prevent a lot of problems.
One thing overlooked in plug changes is the boots from the COP's to the plug itself. If they're hard or stiff, show any signs of cracks or splits then they're cheap enough to warrant replacing with a quality part--I like NAPA/Belden's myself. Should a COP itself go bad the OEM's are superb quality, my 2000 with 285K miles is still running the originals. Again there's no benefit to some gee whizz brand promising improved this or that----the performance aspects are controlled by the PCM.
So anyway that's what I know----glad to answer anything if needed or wanted.