Also wonder about the proxy thing. Sounds like squid in offline mode would be broadly similar?

https://www.oreilly.com/library/view/squid-the-definitive/05...

You'd have to mitm ssl unfortunately:

https://wiki.squid-cache.org/Features/MimicSslServerCert

As for proxy switching, in addition to command line options, there's

https://chrome.google.com/webstore/detail/proxy-switcher-and...

Very convenient for using ssh as a socks5 proxy, for example.