chef_locker
chef_locker is a Ruby gem that contains a script to prevent Chef clients from converging.
To install, declare something like the following in Chef:
chef_gem 'chef_locker'
To run the script, try something like the following in a screen/tmux session:
$ sudo /opt/chefdk/embedded/bin/chef_locker 'Testing CDN host change'
Wait until Lock acquired appears.
Note that if something like rvm is installed, you may have to create a wrapper script to unset some Ruby-related environment variables.