Just wanted to say something regarding HOPO-Cidal Maniac.
If you play a song and at the stats screen hit yellow to replay that song, the HOPO counter in the corner seemingly will revert back to however many you had before you played the song the first time.
Luckily though, this seems to only be a visual glitch. I had around 51,700 HOPOs and played Less Talk More Rokk, which brought me up to around 52,800. On the stats screen I hit yellow to replay it, and when it restarted the song, the counter was back down to 51,700. After the song, the counter was back around 52,800 again, but it gave me the achievement anyway, so it seems that behind the scenes it is still counting all of your HOPOs.