Yes, this is possible.  We can add additional solar as a zero-export system.  The new solar can not export any power to PG&E, while your existing solar can export as much power as needed to PG&E and remain on NEM 1 or 2.  The new solar has special controls (PCS) that can throttle the solar output so it does not exceed your usage.  Batteries can also be added to store energy when producing more than using.  These are complex systems to model properly, which we can do.  Zero-export systems typically make financial sense if your using a lot more energy than your current solar is producing.