Well, you have right idea but it is not class code but 5C copy protection. Do not confuse this with Broadcast Flag which is totally different. Using 5C system they can send flags which tell the recorder that it is copy free (all broadcasts right now), copy once (in use in Japan on Wowow channel which is like HBO here) or copy never. 5C agreement only allows copy never flag to be used on PPV. HBO and pay channels can only use copy once. Executives from HBO and Showtime stated not too long ago that they do not plan to use any flags for foreseeable future.
As far as DVHS HD recorders, all of them including first one from Panasonic which came out in 1999 support 5C. This goes for recorders sold here and Japan. There was a rumour that Toshiba DVHS (already discontinued) sold in Japan could bypass 5C if tracking was adjusted slightly, but I never found any confirmation of that.