If you like, you can specifically ask to keep the HD Value Pack, and also keep the old Sports 1 pack, if you want RSN in SD.
There's not much impact in changing to the new HD pack at the same $10 rate, and an agent won't be too interested in converting you if he/she can't convince you to take all 5 HD themes for $15. Just make sure they keep the old themes as is. You should NOT be forced to update that programming if you don't want to, but it's minimal impact if you do.
And if you do change over, don't choose RSN HD as a pick and pay - for $2.50 more, you can have the 4 HD themes.