If they are the same model (Premiere or Premiere XL) you can do that under "normal" circumstances (using MFSTools, etc). However I don't know that it's been tried with Comer's upgrade method so you're in uncharted waters. I don't know of any reason it wouldn't work though. However when you boot up you will almost certainly receive an error message (as the OEM drives are matched to the unit). You will then have to run Clear and Delete Everything. That will restore the default image. Since you'll basically have a "new" TiVo you'll need to get your cable cards re-paried, etc.