Depends a little bit what kind of file you would like to use.. It is possible to use "Source IP matches IP or Alias" as a acl.. for which you then can create a alias in pfSense with IP's and subnets to match against.. But if you want to specify a domain>certificate or domain>backend 'list' or some other option that needs loading from file (besides a few things like lua and errorfiles..). Then the webgui is the thing that doesn't really 'support' it..
Haproxy binary itself is should have most if no all features described in the manual..
I remember when I built my first pfsense. I just started adding every feature that looked cool and later realized that most of it I didn't need at home. Squid and clam av were among those that I found not very useful for my home scenarios. My clients were either windows which had far superior AV or linux systems which need no AV. So, I don't use those now.
There are scenarios where it is useful though. For me, I used it to control what my kids could see on the net.
Later when they reached their teen years I turned it off…
looks like this is gonna be a manual process by editing the squidguard.conf manually but still won't work because we cannot edit the squidGuard.conf because it is generated automatically with SquidGuard configurator.
I think the best way to force YouTube and google into safe mode is to use DNS overrides. This is what I have on my network. The rewrites rarely work anymore as everything is HTTPS.
Would it be possible for someone to move this into the Packages > Cache/Proxy section of the forums - I should have looked around more before I posted it here. Sorry.