I think the OP wants to manipulate a YAML file with a Perl script (according to the title of the post), so yes, please do check out the various YAML handling modules on CPAN.
- simple and leight-weight and good for most cases. You would read the YAML file into a Perl data structure, manipulate the data in there and then dump it to a new YAML file (or overwrite the existing one). Have a go and post your code here if you are running into trouble.