How can you additionally configure an already running virtual machine using Terraform?.

To further configure an already running virtual machine using Terraform, you need to:

1. Update the Terraform configuration by adding or modifying the necessary parameters of the virtual machine resource.
2. Run the terraform apply command, which will compare the current infrastructure with the configuration and make the necessary changes.

It is important that the Terraform state is up-to-date and matches the actual state of the infrastructure. If the VM was created outside of Terraform, it must first be imported into the state using terraform import.

Thus, Terraform allows managing and modifying existing resources declaratively, applying only the necessary changes.