Adding custom config properties programatically

[Satyanarayana Jampa]

Hi,
                I would like to add "custom core-site" properties during 
installation programmatically.
                Can you please help me out with the necessary info.

                Say for ex:
                                Under HDFS TAB --> Custom core-site
                                                hadoop.proxyuser.root.hosts=*
                                                hadoop.proxyuser.root.groups=*

Thanks,
Satya.