You can always be charged with a probation violation later. You have no right to an indictment on a probation violation. I'm not from California, but it is almost a certainty they will try to violate you for the new similar offense. Depending on the prosecutor and the court, the PV usually will follow the new charge and the new charge takes precedence. I've successfully argued that pushing the PV denies the defendant the opportunity to testify in his own defense because of the right to remain silent in the new charge.
PC 666, or petty theft with a prior theft offense where time was served, may be filed either as a misdemeanor or as a felony. It is a serious charge and will result in a motion to revoke your probation. You need the assistance of a CA lawyer.
Many times the District Attorney will charge less, more, or completely different offenses than what a defendant was booked/arrested on.
A probation violation is not a new charge, but rather is the old case of which you are on probation for. The burden of proof for a probation violation is much lower than that for the new charge. Often the probation violation for failure to remain law abiding (i.e. getting arrested on a new charge) is the biggest problem when trying to avoid custody,