Well, you can believe everything you read on the internet or you can believe the Official Chevrolet Shop Manual that I posted. It even gives a reason.

They dont put caution in all caps and bright yellow for fun.

Just to clarify.

Attachment 20043

What all "thread sealers" , including teflon tape do is make it easier to twist in, thus defeating the torque spec. They also do fill the gaps that are left between the threads, like nail polish.

Note #2 in the procedure "on the spark plug BOOTS".

Is it better to change them on cold or warm engine?

Cold.

But they come out easier if just warm; so run it a few minutes then let it cool down, not really cold. Really doesn't make a difference except for easier to unscrew.

True on that - I've changed them even when hot, due to needing to rush the job - downside was one then had to juggle the HOT plug once removed.

Just replace them on cold engine. I had to apply a little bit of force to get them going. They cooked up a bit after 76k mi. Here is what they looked like:

https://www.chevyhhr.net/gallery/fil...915_101516.jpg

What would be the major problem with over torquing the plugs. I assume that the person who is changing them is not a complete idiot and is not going to apply more force than 20 - 25 lbs. I don't think this would be sufficient to actually strip the threads. However, it may lower the plugs far enough to cause damage to the piston once the engine is turned on. Correct me if I am wrong.

Aluminum heads/steel plugs; do the math.

Flat rate guys don't do anything by hand, they use air impact tools whenever the can.