1. A computer implemented method, comprising: providing a host computing device operated by a service provider of a service provider environment, the host computing device including an agent configured to run in a first domain managed by a virtual machine monitor of a virtualization subsystem of the host computing device and the agent configured to perform modifications for a second domain of the host computing device; receiving a request from a service operating in a service provider environment at the host computing device to configure a guest operating system stored on a volume, the guest operating system associated with a guest machine configured to run in the second domain, wherein the guest machine is associated with an account of a customer of the service provider; mounting, by the agent, the volume; modifying, by the agent, configuration files stored on the volume to add or remove data as specified in the request while the guest operating system is offline; un-mounting the volume and attaching it to the guest machine; and causing the guest operating system to boot, the guest operating system configured to incorporate any changes made to the volume during the boot and modify at least one behavior of the guest operating system according to the changes.