First of all, You really should use CGI.pm, strict, and warnings. With that said: you can easily modify $sign_msg and then join all the variables back one string.
($number, $sign_name, $sign_email, $sign_homepage, $sign_icon, $sign_t
+ime, $sign_msg ) = split ( /__/, $line ) ;
$sign_msg = "Hello, World!\n"; # Do your modification here
$newline = join ( /__/, ($number, $sign_name, $sign_email, $sign_homep
+age, $sign_icon, $sign_time, $sign_msg );
push @newarray, $newline;
-Ben Jacobs (dooberwah)
"one thing i can tell you is you got to be free"