This is a bad idea if your goal is to be productive and use the tools. But you can learn a ton by disabling SIP on a machine you don’t need and seeing what breaks when you modify the tool. If your goal is to learn, go for it. Here is why it’s “bad” and some very good resources on the history of where to add customizations on unix.
Apple protects /usr via system integrity protection and the closest place to / that’s encouraged to write files is /usr/local
Package managers (and the people that write and spend a lot of time using them) can be as passionate (and sometimes prickly) in terms of preference as those debating text editors like [ed|sed|vi|emacs] as well as newer programming editors with more graphical basis.
- What is standard for OS X filesystem? e.g. /opt/ vs. /usr/
- Has Unix directory usage or policy changed in High Sierra?
- Where should I install new (source code) software on a Mac?
This answer particularly has some good thinking and clear discussion as well as the above questions. There would have to be a very compelling basis to diverge from the standard for homebrew even if you didn’t but heads with Apple on SIP in the process (which is what happens in /usr).