You reduced the felony per California Penal Code 17(b) and then expunged it purusant to California Penal Code 1203.4.
No, you cannot answer "no" on your application. There are specific exclusions to the power of expungment under 1203.4 and the applicaiton for work in law enforcement is one of them. You will need to tell them about your conviction (they will see it on your record).
This doesn't mean that you can't be a police officer. I would call whatever agency you eventually want to work for and ask them what your chances are.
You must disclose the conviction in any peace officer application. You will also be required to provide a detailed statement of all of the facts and circumstances underlying the conviction.
Most but not all jurisdictions will allow you to apply for employment even with this degree of criminal record history. But, in candor, the potential for you to be offered peace officer employment is extremely low. You must understand that this is an incredibly competitive job market, and every law enforcement jurisdiction has multiple applicants for every position. Most of those applicants have no criminal history. It will be very very difficult for you to compete effectively against so many candidates who have no criminal record.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.