This part of the document William linked seems relevant to my renaming needs,
but I can't figure it out:

"  Details: User-defined option N
    %[param] param variable in query string

This new option is important: you can include query-string content when
forming the destination filename!

Example: you are mirroring a huge website, with many pages named as:
www.foo.com/catalog.php3?page=engineering
www.foo.com/catalog.php3?page=biology
www.foo.com/catalog.php3?page=computing
..

Then you can use the -N option:

httrack www.foo.com -N "%h%p/%n%[page].%t"

If found, the "page" parameter will be included after the filename, and the
URLs above will be saved as:

/home/mywebsites/foo/www.foo.com/catalogengineering.php3
/home/mywebsites/foo/www.foo.com/catalogbiology.php3
/home/mywebsites/foo/www.foo.com/catalogcomputing.php3

"

%h is the www.foo.com part; %p is the catalog part; %t is the file type.  What
does the /%n%[page] part do?  And what exactly does the -N part do (is it just
a naming command, or does it do more?)?