Anyone else require the need to pitch the gimbal during DJI Pilot mapping mission with the M300? What are you using the system for?
Software only lets you fly with the gimbal at 90 degrees straight down (NADIR)...

You probably won't have much luck with the Mapping Mission approach. If you open an exported Mapping Mission KML with a text editor, you won't see the "gimbalPitchMode" option that you get with an exported waypoint mission. As you have found, there is no option I see to release automatic control of the gimbal settings in the Mapping Editor.

Since an exported Mapping KML doesn't have the Lat/Lon values of the actual grid line end points, I suspect that you're not going to be able to get around this problem without a DJI Pilot software change from DJI.

UGCS would allow this level of gimbal control, but there are a bunch of new problems that come up in terms of apps installed on the smart controller, local networks in the field, and license verifications. UGCS will fly an M300RTK, though.

The only other suggestion I can make is to measure the grid widths you get for a mapping mission, then make a Waypoint mission KML where you can set the "gimbalPitchMode" value in the wayline section.

I have used this before to get around the single focus point problem with mapping missions, but without an automated procedure it would be very tedious to do by hand.