In a perfect world such things would not be necessary.
# *sigh*
brew tap bryonbean/homebrew-php56 git@github.com:bryonbean/homebrew-php56.git
brew reinstall php@5.6My multiple versions of php were originally set up by way of this great post. I should have checked it before creating this because the author keeps it up-to-date in spectacular fashion. Sure enough it seems that there is already homebrew-deprecated being maintained which services both php@5.6 and php@7.0.
brew tap exolnet/homebrew-deprecated