I just called and asked dish about the turbo HD. The guy said it was only for new subscribers. I would imagine you could update your current programming.
I could see it offered as a "downgrade" as some people cancel or want to scale back for $$$ reasons. I know the local Time Warner has a low-end RoadRunner package for people who call to cancel their RR service, but this package isn't advertised anywhere. And for a long time, they wouldn't mention their "basic" cable package, i.e. channels 2-25 or so, unless you knew specifically to ask for it.I suspect they will be willing to give you it as an UPGRADE, but not as a downgrade.