The coil boots are a replacement item when plugs, particularly long-life iridiums, are changed. Rubber stuck into the cylinder head doesn't last forever, or at least not 16 years.
If your new wireset isn't already, try siliconing the rubber grommet to the extender tube thing.. some wiresets I've bought in the past had this done to prevent that exact thing
Go job getting that out. Get a set of these or similar long ones, they are just the thing for this sort of work. I got them at Sears years ago, it looks like they still carry them.
Great! I'm glad it worked out for you. Just an added thought. When you go to buy new wires or replace the boots, (if that's possible), be sure to get Silicon wires and or boots. They are much more impervious to drying out from heat degradation.
I've been through this many times.
I had to change plugs in a car that had the same type of boots.
The plugs had been in for 100K miles.
When i couldn't get the boots off with moderate force i stopped.
I thought heat usually loosens most things.
So i warmed the car up and the boots came off very easy.
And yes I let it cool down before changing the plugs so as not to damage the threads.
The boots good a good dose of dielectric grease.
And guess what? Fast forward another 100K and the boots came off easy and with the engine cold.
And yes it was my Sentra.