Populate Default Text for Text Boxes

you could use Workitem Templates as well.. but that needs creation of one dummy workitem with the default values for all those attributes that needs to be initialized when a new workitem is created. 

the template is created in eclipse client.  right click on the dummy workitem and choose "Create Work Item Template".  The template is saved and is available from the Work Items menu > Create From Template... menu item in the web client

See 'Customizing attributes in Rational Team Concert 3.0' (https://jazz.net/library/article/537), 'Default Values' section to achieve this.