Downgrade homebrew (cask) package

change_vagrant_version_brew.sh

# Uninstall current version you want to change
brew uninstall --cask vagrant

# e.g. Vagrant
brew edit --cask vagrant

# replace the contents of that file with the version of the file found in github history:
# https://github.com/Homebrew/homebrew-cask/commits/master/Casks/vagrant.rb
# or change version and SHA256, you can find on https://releases.hashicorp.com/vagrant/
```
cask 'vagrant' do
  version '2.0.1'
  sha256 '07f7be3a457a8422d576e6371c8499fbdea411b02aecc7ea3c5258494514c5f2'

  # hashicorp.com/vagrant was verified as official when first introduced to the cask
  url "https://releases.hashicorp.com/vagrant/#{version}/vagrant_#{version}_x86_64.dmg"
  appcast 'https://github.com/hashicorp/vagrant/releases.atom'
  name 'Vagrant'
  homepage 'https://www.vagrantup.com/'

  pkg 'vagrant.pkg'

  uninstall script:  {
                       executable: 'uninstall.tool',
                       input:      ['Yes'],
                       sudo:       true,
                     },
            pkgutil: 'com.vagrant.vagrant'

  zap trash: '~/.vagrant.d'
end
```

# Then reinstall brew package
brew reinstall --cask vagrant

# check correct version with
vagrant --version

# update and repair plugins now that you've changed versions
vagrant plugin repair && vagrant plugin expunge --reinstall