Interactive mode in Nmap allows users to press keys to dynamically change the runtime
variables, but when this book was being written, there weren't any official patches available.
However, there is an experimental patch, which was submitted in June 2012, that allows you
to change the values of --max-rate and --min-rate dynamically. You can find this patch
at http://seclists.org/nmap-dev/2012/q2/883.