This only addresses your last question, but I have found several other minor differences. In this answer there are two quotes from The Last Guardian that have very minor differences.
The first one is from Chapter 11. This is the version quoted in the answer:
Opportunity had presented itself to Opal when her younger self had
made telepathic contact.
One morning Opal had been deep in a cleansing coma and - ping! -
suddenly there was a voice in her head calling her sister and asking
for help. It had occurred to her briefly that she could in fact be
insane but, little by little, the information filtered through. A
younger Opal had followed Artemis Fowl back from the past.
However, the Disney-Hyperion edition has a slight difference:
Opportunity had presented itself to Opal when her younger self had
made telepathic contact.
One morning Opal had been deep in a cleansing coma and - ping! -
suddenly there was a voice in her head calling her Sister and asking
for help. It had occurred to her briefly that she could in fact be
insane but, little by little, the information filtered through. A
younger Opal had followed Artemis Fowl back from the past.
Notice how in this version the word "sister" is both capitalized and italicized. The answer does not say which edition it used, so it is hard to confirm whether this is an actual difference, or just a transcription error in the post. However, the one version that I found online, has a third variant in which the word "sister" is capitalized but not italicized. Although, a closer look seems to show that that there are no italics at all in that version, so that may just be a formatting issue with that particular site.
It should be noted that the second version probably makes more sense in context, as the capitalization/italicization show that the word "sister" is a term that Young Opal called Old Opal. Without it, the sentence could be read as referring to Opal's sister which would be inaccurate.
The second difference comes from a quote in the same answer, from Chapter 1 of The Lost Guardian. The version quoted in the answer is:
Cloning was a banned science both for religious reasons and the more
obvious fact that, without a life force or soul to power their
systems, clones were doomed to a short life of negligent brain
activity and organ failure. This particular clone had lived out most
of its days in an incubator, struggling for each breath since it had
been removed from the chrysalis in which it had been grown.
However, the version in my Disney-Hyperion edition is:
Cloning was a banned science both for religious reasons and the more
obvious fact that, without a life force or soul to power their
systems, clones were doomed to a short life of negligent brain
activity and organ failure.
This particular clone had lived out most of its days in an incubator,
struggling for each breath since it had been removed from the
chrysalis in which it had been grown.
As you can see, the last sentence has been made into a new paragraph in the second version. This time we can confirm that it is a real difference, because the version on Google Books does not have the paragraph break. However, to make matters more interesting, the version on Google Books is also Disney-Hyperion, so there might be different versions even within the same publisher,, or perhaps
Google Books messed something up.
Here is an image of the version which has the paragraph break:
Another difference is how the titles are written. In the United Kingdom editions the books are all called Artemis Fowl and the... while in the United States editions the books are called Artemis Fowl: the... (i.e. without the word and). You can compare, for instance, the United Kingdom cover image with the United States cover image of the sixth book.
Another minor difference between editions also appears in the sixth book. In Chapter 4 the Disney-Hyperion edition has the following sentence:
He selected Beethoven's Symphony No. 7 from his vast selection of
mental music and listened to it as he thought.
In the edition on Google Books, though, the sentence appears like this:
He selected Beethoven's Symphony N o 7 from his vast selection of
mental music and listened to it as he thought.
I.e. there is no period after the "o", and the "o" is written as a superscript instead of as regular text. This same difference also appears in Chapter 14 when referring to Symphony No. 8.
Additionally, right after the mention of Symphony No. 8 there is a section heading. In the Disney-Hyperion edition the heading says:
The Present
In the version on Google Books there is a more expansive heading:
FOWL MANOR, THE PRESENT
Other section headings as well are in all capitals in the Google Books version but not in the Disney-Hyperion version.
