This is a fabfile for people who prefer to work with Scientific Linux distribution, but their hosting/cloud provider can only provision CentOS boxes (e.g. Linode).
First of all, it will set up a correct time zone for you and sync the time with the ntp server. Next it will perform the steps gathered from here. It is recommended to do this procedure on clean box only. The conversion of already-in-production boxes wasn't tested.
I've created a test t1.micro AWS instance using one of the minimal CentOS 6.2 AMIs (ami-1fa4a16b in the european region) and ran this fabfile against it. For a CentOS 6.2 to Scientific Linux 6.3 conversion it took almost 22 minutes.
First of all you have to install fabric. Here's the easiest way to install it:
$ pip install fabric
Then you should set the desired timezone in the fabfile. Replace the "Europe/Moscow" with what you want. Right after that you can fire up this script, replacing USER with your AWS ssh user and HOST with your AWS host:
$ fab -H HOST --set user=USER main
Your user should have a passwordless sudo permissions or you will need to add --set password=PASSWORD to your command line.
It's recommended to reboot your host after a successful conversion.
Right now the fabfile has two hardcoded URLs for yum-conf and sl-release packages. So if those will change, the fabfile will require an alteration of those variables.