You can use data tidy to set default values for your fields. Select 'Tools' on the menu bar at the top of Management, then select 'Data Tidy' from the list. Use the menu to select which field you would like to set the default for and enter in the required value at the bottom of the page.
Finally, click 'OK' to save the changes. Now, every resource you catalogue that has this field available, will have this value automatically added.