We have contentregexplist file where we can write all substitutions like "source regex"->"dest string"
And they ALL run for each page. Is it possible somehow to define a domain name(s) for which (only for 1 domain! not every page) some regexps should be looked for?
To be clear:
How to replace "Google"->"garbage" in page source only for host host.example.org?
May be other content filtering system can do this? Then which one?
No, dansguardian cannot do this with content modification rules. You might be able to write your own squid helper to do it.
I know Smoothwall is able to 'target' content mod rules (disclaimer: I work there) with their latest content filter - which is based on dg-like principles (The Dan is our CTO) but is a complete rewrite.