You can change default values for any user-defined creative template, including for any template made by us. But this must be done carefully to do not break template functionality.
Here is the list of fields you can change:
Changes to "Reporting" options and other fields that not mentioned above can break a creative template functionality.
Please remember, all changes will be lost after any further import. Make a copy of your changes before import if you want to update changed values to the previous state after new import.