in Mac OS 8 and 9, you could patch the system direct. OS X was harder, and became sprawling and interdependent, encouraging users to reinstall macOS. That has now ended with the introduction of the SSV.
Pacifist
How can you install older drivers or other software on a new Sierra system? Some practical tips for working through SIP and security protection.
I want to give my old Mac away, but it has lost the Mail app. How can I replace that?
Just when most software had settled on using Apple’s Installer, along came the App Store to add to complexity. And then there’s Adobe with its own downloaders and installers again. So how should we install and update software?
The Eclectic Light Company 