When ever you create a new application pool IIS only asks you for four things 1. Name, 2. .NET Framework version, 3. Managed pipeline mode and 4. Weather to start the application pool immediately
What about the remaining advanced settings like the identity that application pool has to run under? The application pool inherits the rest of the settings.
If you want to change the default settings that IIS uses to create a new application pool you can do it under the Set Application Pool Defaults… section
For example if you change the Managed Pipeline Mode to Classic in the defaults and add a new application pool the mode dropdown will be set to Classic.