yeah the sidelight bulb holders are fairly solid fit. I changed mine the other day, just used a small flatheaded screwdriver to lever it out. Comes out very easily that way.
Make sure they go back in properly as it takes a fair bit of force to push them back in again.
I ordered them about 2½ years ago now when I had just taken delivery of my 172. Am still using the same set in my Trophy now. I did get the free set of sidelight bulbs then too, although they stayed on my 172 as i couldnt be bothered to remove them.
Just replied to your PM Mike, i'll post what i said here for the benefit of others.
The bulbs above are the Silvervision indicator bulbs rather than headlight bulbs. These remove the orange tint from the light clusters as although the bulb still flashes orange, it's silver when not illuminated. Makes quite a difference to the appearance of the car in my opinion.
If you want a xenon effect to your actual headlights (i.e. a more pure white light rather than the yellowy tint of standard headlights then there are a couple of options.
1. You could simply replace the bulbs with some higher quality xenon gas filled bulbs such as Osram Silverstar which are also available from the powerbulbs website, or for a more blue look then there's the Philips Blue Vision
2. If you really want what most people mean when they say 'Xenon headlights', then as you thought, you'll need to get a HID (High Intensity Discharge) conversion kit. The Xenon lights as on the full fat 172/182 do not have a light bulb with a fillament that glows, they use high voltage to create a continuous spark between two plates.