What you'll have a hard time changing the gap on is the Bosch plugs. They have four ground electrodes coming in from the side, like aircraft spark plugs. This works great for long life since when one electrode wears, the spark will jump to the closest one. The center electrode is not covered, since they come in from the side.
The Denso plugs are conventional, except that the center electrode is very thin (like mechanical pencil lead - less than half a mm). It is very hard and wears well. It gets gapped like a conventional plug. One should never leverage the gap tool on the center electrode to push the ground electrode up.
The spark plug gap has to do with the current and voltage put out by the coils. Modern ignitions put out much more energy and can jump a larger gap. A larger gap means more area for the fuel to ignite.
From Denso's FAQ:
"
Q. Do I need to set the gap? A. Generally, no. The DENSO Iridium Power plug comes pre-set with a protective sleeve over the firing end, to protect the gap from accidental alteration. DENSO Iridium Power’s ultra-efficient firing power compensates for normally recommended
gap settings that are smaller than the pre-set value. In the cases of vehicle modifications (nitrous, turbo-chargers, super-chargers, high power ignition systems, etc.), some adjustments may be desired.
Or, if you prefer to remain consistent with factory specifications, you may adjust. However, please be careful not to place any stress on the fine center electrode during adjustment. You could accidentally break off the very hard, and therefore brittle, tip. "
Apparently, you can either leave them at the factory gap, or gap to your cars factory spec.
