I tried to change log format and change HTTP_REFERER using perl to change browser's referrer like below.

[pattern1]
Log Format : %{HTTP_REFERER}o
perl       : $ENV{'HTTP_REFERER'} = "http://www.google.com";

[pattern2]
Log Format : %{X-RT-REF}o
perl       : addHeader('X-RT-REF' => "http://www.google.com");

[pattern3]
Log Format : %{HTTP_REFERER}e
perl       : $ENV{'HTTP_REFERER'} = "http://www.google.com";

but they didn't work. How can I do it? If you have any idea please teach me. Note that I just want to do this as a countermeasure for illegal access in my intra tool.