> I know that HTTrack rewrites the filename using an md5 of
> the query string. But can't it use simply the query 
string?> page?param1=value1&param2=value2 as
> page.html@param=value&param2=value2

The file won't be useable anymore by the Windows explorer 
(bad extension)

> illegal filename chars with legal ones, it preserves the 
url
> and it make it easier to parse them. 

Note that the original query string's URL is preserved.

> How can I make HHTrack name files with the query strings? 
Or
> if I can't, is it possible to implement it? Seems to be 
very
> simple to do it.

There is no simple way - the simplest one is to make a 
small plugin (.dll or .so) that will handle file renaming - 
see callbacks-example-filename.c and callbacks-example-
filename2.c in the libtest/ directory of the source archive.