Homebrew and existent software in /usr/local Is it ok to install homebrew in default(for homebrew) deirectory /usr/local if I've already have installed software there.

In other words, if Mysql and GPGTool already installed in /usr/local and then I'll install homebrew also in /usr/local. Will it work correct or I should install homebrew in another directory.

P.S.: I know that homebrew has mysql but I need special version that already installed.
It would probably work ok to mix the two, but to be safe I'd just put homebrew in a different directory.  You might run into conflicting files, perhaps in some supporting library.

I don't know what's special about your mysql build, but i'm sure homebrew has options to build different flavors.  do "brew options mysql" to see what is available, perhaps it has what you need.