At one time espher was speculating it might be possible to toy with on-disc songs using the Rock Band Harmonies Project tools, and he starting compiling a list of possible fixes. But his time and attention have since been diverted to More Important Things (no sarcasm ” data-emoticon=”” src=”/emoticons/default_SA_smile.gif” title=”” />), so nothing more has come of that.
Like Alternity said, any such trickery would likely involve injecting new DTA information into the song cache, or manipulating the cache directly. Based on what (relatively little) I know about the cache, changing things like song and album titles might not be that hard, once you’re comfortable hacking the cache. There is even a cache modding tool available on the forum here, though I think it’s mostly intended for the XBox 360 cache file. Changing album art would likely be trickier, since you’d also have to supply the art file. Changing charts would be the trickiest of all, since those are not stored in the cache, but are read directly from disc (or hard drive) every time you play that particular song. It still may be possible with some sort of clever redirects within the cache data, but at this point there are no guarantees.