create entries in Portalapp.xml

How do i programatically create entries in portalapp.xml file?

I need to create some profile properties inside this file dynamically.

<component-profile>

<property name="myColor" value="red"/>

......

.....

I know, how to read and set the values but how wud i go about creating a new entry?

EG: <property name="yourColor" value="green"/>

from the Dynpage.

Thanks.