Tonight I decided to go ahead and take apart the shift knob/boot/trim on my Focus, to figure out the procedure. Searching forums showed lots of questions but no definite answers for taking everything apart, nor were there any for the thread pitch of the shift knob.
So, here's how it went:
First, remove the trim piece around the base of the shift boot. There are clips all around it, but the ones that really hold it down are located in three of the four corners (The corner missing one is the rearward passenger side, next to R). By gripping the trim piece through the boot, some firm tugs and pulls should see them pop out, one by one. I shifted through a few gears to reposition the shifter, giving the boot extra slack when needed so that I didn't stretch it. For undoing the knob, grip the top of the boot to prevent it from spinning and start unscrewing. It can take a fair bit of effort to get the knob to start turning.
When the whole assembly is out of the way, this is what's left:
This is everthing that came out, taken apart.
The boot clips to the underside of the trim. It's very easy to remove and clip back in - the boot itself is pretty much permanently mounted to the plastic base that allows it to clip in though. An aftermarket boot would probably have to be attached to this base (With the original boot cut out) if you're looking for a quality, OEM-looking install.
The shift knob is held to the boot via a clip that sandwiches the top of the boot between itself and the base of the knob.
Said clip sits here on the boot (Looking from the inside)..
..and the knob then pops in here.
After figuring out the removal and installation procedure, next was to measure the thread pitch. I'm brand new to Focuses, so I didn't know if it's be the same as previous generations or not. I measured it as 12 x 1.25
So anyway, that's what I discovered in my trial tonight. Now that I know how, and the thread pitch, I can go pick a nice new shift knob for the Fofo. Hope this helps!