https://toggen.com.au/it-tips/hide-your-squid-proxys-internal-hostname/

# add this to /etc/squid/squid.conf
visible_hostname mybogusproxyhostname.local
# and while we are at it stop squid blabbing about it's version aswell
httpd_suppress_version_string on

# then restart squid
/etc/init.d/squid restart