Unfortunately, in this case I don't believe the officer has the authority to file this as an infraction. The code section reads:
21651(b) "It is unlawful to drive any vehicle upon a highway, except to the right of an intermittent barrier or a dividing section which separates two or more opposing lanes of traffic. Except as otherwise provided in subdivision (c), a violation of this subdivision is a misdemeanor."
The code itself specifically states "a violation of this subdivision is a misdemeanor" and therefore precludes the option of it being filed as an infraction. The officer has no authority to circumvent the code by filing it as an infraction and the court on its own motion cannot amend the citation. So, the only option is that the citing officer file form TR-100, Notice of Correction and Proof of Service to change the violation to 21651(a).