On the surface changing plugs is simple but if done improperly it can open up a real can of worms. If you use a slow, methodical approach you should be fine. Here’s a few tips.
Remove the old plugs slowly. If one feels very tight then try snugging it up a bit tighter before trying to loosen it again. In other words, seesaw it a bit if have to do so.
When removing a coil do not pull it straight off. Try to wiggle it back and forth as you pull.
Check the gap on the new plugs and CAREFULLY adjust if needed. Do not ASSUME the gaps are correct as they are often not.
Use anti-seize on the threads of the new spark plugs.
Use dialectric grease on the inside of the coil boots before reinstalling the coils onto the plugs.
When installing the new plugs do NOT use a socket and extension. Use a short length of fairly stiff vacuum line that has an inside diameter small enough to create a tight fit on the end of the spark plugs and start them into the threads by that method. This assures that you will not strip or cross-thread anything.
Snug the plugs up by hand. Most long time mechanics tighten plugs by feel as that is far safer than a Ft. Lbs torque wrench or following shaky specs given in a manual. All that is required of the plugs is to run them down all the way and then give them a fraction of a turn.
Ignore the comment by the dealer about 3 grand if you cross them up. This sounds like yet again a shop that apparently does not have any clue what a thread insert or Heli-Coil is.
No doubt a service writer is the person who stated this to you. NEVER listen to these guys; and in some isolated cases these gals.
(Inserts and HCs are used to repair stripped threads and unfortunately, it seems like far too many mechanics and shops now seem to think the proper fix is to replace cylinder heads or complete engines after you float a homne equity loan to pay for it.)
That’s the proper method. An improper method would be the young tech at the dealership who will rip those babies out quickly with an air ratchet and ram the new ones home by the same method after cranking the air pressure on the ratchet up to MAX. Hope that helps anyway.