How to open a blocked site from the blacklists

• Login into the Squidguard server.
• su - proxy (better avoiding root account)
• cd /var/lib/squidguard/site_perm/
• edit domains file and add the domain to be opened.
• edit domains.diff file and add the domain to be opened with a + at the beginnig (ex: +my_domain_to_open.com).
• run squidGuard -u
• rm domains.diff
• exit from su
• invoke-rc.d squid reload

and how to close it

As above, only use the /var/lib/squidguard/site_blocked/ as working directory.