Is there a way to attach a L-7 policy to an iApp which uses appsvcs_integration_v2.0.004 template ?

You can attach a Traffic Policy to the integration services iApp that was previously created by utilizing the field "vs__AdvPolicies" in the REST call, utilizing the deployment scripts using the same variable name in the input file, or you can also specify it in the "Virtual Server: Advanced Policies" section in the iApp gui (Keeping in mind, the better way to modify this is to utilize the provided deployment scripts or a REST call.)