If you want to be evil and have written any GPL you can sue everybody in the target country that uses your software. Since the GPL isn't legal in their country residents of that country have no legal right to use your code. Note that you need to write "mass market software" for this to apply.
Of course I'm not a lawyer, consult a lawyer if you need legal advice.
>This part of the sentence limits the application of the rest of the paragraph to software that crosses the border into the country in some way or another.
No, the word "or" is the operative one here. So if you deleted the word "import", it wouldn't matter. Yes, the law applies to imported software, but it also applies to any software which is distributed in its territory, or sold in its territory, etc. No border-crossing is necessary.
My cursory understanding is that the GPL becomes more like the BSD or MIT license in that it becomes lawful to distribute altered binaries without the corresponding altered source code.
However, legal texts are tricky and the correct interpretation of this one my well be different from my current understanding.
Edit: -----
After rereading parargraph 1 another three times, I think that the wording of the text suggests a far broader scope than it actually covers.
"...as a condition for the import, distribution, sale or use of such software, or of products containing such software, in its territory."
This part of the sentence limits the application of the rest of the paragraph to software that crosses the border into the country in some way or another. The sentence also begins with
"No Party..."
where parties are the countries (represented by their governments). So this is about government regulation of software that somehow gets into the country some way or another.
" shall require the transfer of, or access to, source code of software owned by a person of another Party"
With all the preconditions above in mind, this actually means that no government can impose rules on somehow imported software that would require the seller in another country to provide the source code with the product. Effectively, this is only a restriction on lawmakers. Individual persons and companies are not directly affected this section of the treaty.