I just want to check to make sure there isn't an easier way to do this.  I live in a hilly area of Northern California.  Where I take off, the elevation is about 850 ft.  When I fly out, I sometimes have to cross ridges that are at 1200 feet.

The DJI software imposes a limit on my max altitude.  I know I can override that, but I am wondering if there is a way to have it automaticlly change the max based on the ground elevation that it gets from its database, or better yet, from the under-belly sonic transponders or cameras.

I like having the max altitude there to keep me from going too high.  I'd like to remain at or under 400ft AGL, but right now, I have to stop and change the max altitude each time I get to these other ridges, and then remember to change the value back when I am not flying over higher elevations.

Anyone have any tips/advice?

To my knowledge the maximum altitude is measured from takeoff point, which would give you room up to 1250 ft when taking off from 850ft.
If that's not enough I'd just permanently change the default setting and keep my eye on the altitude meter, like I do on my speedometer of my car or bike.