I needed to build a new Foreman / Puppet master as a prelude to upgrading
Foreman 1.2 to 1.4.
This was on a CentOS 6.4 VM so the first part was easy just take a clone
and give it a new hostname.
This may not be the best way of doing this: If you know of a better way
please let me know.
My steps - they may not work for you - so no guarantees so take backups.
First take a BACKUP. I was working on a clone so the old host was my backup.
Stop Puppet & Foreman.
service httpd stop
service foreman-proxy stop
Then edit the following files to change the hostname.
/etc/httpd/conf.d/puppet.conf
/etc/httpd/conf.d/foreman.conf
/etc/puppet/puppet.conf
/etc/puppet/node.rb
/usr/lib/ruby/site_ruby/1.8/puppet/reports/foreman.rb
/etc/foreman-proxy/settings/yml
You need a new set of certificates the way that works for me is:
rm -rf /var/li/puppet/ssl/
service puppetmaster start
That generates a new set of CA and Puppet certificates 
service puppetmaster stop
service httpd start
service foreman-proxy start
Login to Foreman and change the name of the SmartProxy and any [global]
parameters that have the hostname.
puppet agent --test
puppet agent --test
After any work on the server I like to force a puppet run and repeat it
until I get a puppet run without any actions.
On each of the Puppet clients that are moved to the new server:
edit /etc/puppet/puppet.conf # To change the server / puppetmaster name
rm -rf /var/li/puppet/ssl/
puppet agent --test
That works for me as my Puppet clients are run via a cronjob and I have
autosign enabled on the puppetmaster.
I hope that it helps if not I hope that it give you some pointers.
For the experts out there if you have a better way please let me know.
Regards, Mike.