Everyone is pretty much right... if you have them, you get to keep them. In my case I had all E & W SD from the beginning before SD locals, and HD West from back before they offered Seattle HD locals (since I already had all the SD's, they also gave me all the HD's)...
Since the HD ones were free and I wanted to save some money and didn't particularly need the East feeds, I dropped all the SD ones except FOX since I still wanted their SD East channel. They said that since I had all the HD distants, I would have no problem getting back the SD ones in the future if I wanted them turned back on.
WELL, needless to say, I added another SD TV and I wanted the distant SD feeds back for that room... Sure enough, I couldn't just add them back so easily... I had to go through the whole waiver thing, even though I have all of them in HD. I already had FOX since it has never been turned off since I got it in 1998, but only NBC said yes to me getting back SD distants (since back in 1998 only FOX needed a waiver which they granted--I was outside Grade B for all the others--which doesn't matter anymore).
SO, I have NBC and FOX SD, and all four for HD distants + Seattle locals... basically if you get them, don't touch them!! I would love to get the Washington DC CW station since they are starting up local news from there, but don't want to risk even asking.
--Nat