No, this does not meet the goal. Unregistering the Microsoft.ClassicNetwork provider does not affect the creation of network security groups (NSGs) in the subscription. The Microsoft.ClassicNetwork provider is used for managing classic deployment model resources, such as virtual networks, network interfaces, and public IP addresses1. However, NSGs are only supported for Resource Manager deployment model resources2. Therefore, unregistering the Microsoft.ClassicNetwork provider will not automatically block TCP port 8080 between the virtual networks.
To meet the goal, you need to create a custom policy definition that enforces a default security rule for NSGs. A policy definition is a set of rules and actions that Azure performs when evaluating your resources3. You can use a policy definition to specify the required properties and values for NSGs, such as the direction, protocol, source, destination, and port of the security rule. You can then assign the policy definition to the subscription scope, so that it applies to all the resource groups and virtual networks in the subscription.