this thread looks about dead anyways at this point.
everything i can find, including the government website, pretty clearly states that offenders with convictions regarding sex crimes will not be able to appeal for a reduced sentence.
http://www.cdcr.ca.gov/news/prop47.html
i think you may be referring to a nebulous hypothetical rather than the written law itself. like, 'what if sex criminal is granted a plea deal for some lesser charge and then gets a reduced sentence based off that charge?'
federally, i can state, they do a pretty good job at fucking you during sentencing. oftentimes, once convicted, the sentence is based on the initial (and more severe) charge rather than the final conviction. that is how you end up with some of the insanely long terms for seemingly minor-ish offenses. no idea how this plays out in a local or state courtroom though.