This warning indicates that by completing this wizard you will actually modify/resave an existing Service Package instance (by name EmailDefault in this case) which might have got other service rules created in it. The modified configurations for this instance during wizard run will be applied to all the services in it (along with the Service-Email rule that you are trying to create in this wizard run).
This warning in wizard not necessarily be avoided. You may choose to continue, if you are not modifying the configurations of service package (the options available in the same wizard screen). Otherwise you may wish to specify a new service package name in the previous screen in order to create it with new configurations.