Some California crimes, known as "wobblers," can be reduced from a felony to a misdemeanor. You can tell if an offense is a wobbler by looking up the punishment in the California Codes; if it says by jail OR prison time, then it's a wobbler. If it only lists a prison sentence, it's a "straight felony" that cannot be reduced.
All of the sales offenses, which are listed in the Health & Safety Code, are straight felonies.
No, it cannot be reduced as indicated in the previous answer.
Assuming you successfully complete probation and are not sent to prison as a result of this case, you can seek a dismissal under Penal Code section 1203.4 (commonly referred to as an expungement). It is of some benefit, but it's not a magic cure or eraser to your criminal history.
The answer to your question is probably "no." An exception would be if, at the time of your plea, a part of the bargain was that you could return to court at a later date to have the conviction changed to simple possession and reduced to a misdemeanor. If that wasn't part of the bargain, then you're probably out of luck. Nevertheless, you may still have this felony conviction expunged.