At this point I'd just say "It is what it is", and stop holding out for a pipe dream of being able to choose to record SD in place of HD. The idea of 1000+ for SD channels seemed gone when they added international channels to the 1000 & 1100 range. If it's a deal-breaker, I'd suggest another platform than the 8300 for your DVR usage. Anything that costs around $18 / month or less would net you the same price and give you the feature you are looking for. The lack of interest from anyone else here for the feature, at a forum with a higher technology-aware posters who would think about (and read this request) the thought of increased storage space from recording in HD, tells me this is not something CV is going to modify.
-You can use an external HD for the 8300
-In a mixed HD/SD environment (unsure if it does in a HD-only environment, but I would suspect it does), DVR Plus allows you to choose if recording in HD only (Default) or for "All TVs" in SD, but they don't need to build channel mappings into the individual boxes for each channel.
-TiVo costs $14.95/month + $2 for cable card, and does not have the HD > SD mapping, letting you choose which to record.