If you're looking for multispectral and not simply converting a single lens from CGO3 with a IR / NIR, your best option is one of several Multispectal cameras that includes an RGB (5th lens) as well. With analysis software & reporting, you'll need to provide actual images overlaid or on same report to provide the data needed.
If the products that support DJI platform don't settle with you, look at other specialized platforms. One being a moderate priced, Parrot Bluegrass full package including Pix4Fields software.
Parrot drones as seen by professionals: discover all the use cases and how our drones are being used to assist professionals.
www.parrot.com
This totoal package integration is helpful with for learning, and obtaining support as you continue to define your ideal setup.
Plus you can easily adopt additional NDVI SW, or move the Parrot Sequoia multispectral camera to alternate platform. Actually you can mount the Parrot Sequoia on the belly of the H520 and mount the light sensor on top and fly the Ag Field with any Map software desired and continue using the CGO3 or E90 as your standard Nav Camera connected to ST16.
Revisiting DJI, the above scenario is basically what is performed on DJI too. You can use DD, UgCS, or dozens of great mapping/Ag/Terrain specific Apps with a multispectral mounted to the belly performing a separate collection.
DJI does not provide their own Multispectral camera... yet, nor focused Ag Terrain app.
If you're wanting to avoid purchasing additional platform, then look into the Parrot Sequoia Multispectral camera... it's offered in several other "Brand" labels or similar models by Ag focused Products. Check out Sentera or MicaSense RedEdge too.
sentera.com
RedEdge-MX The technology you’ve come to depend on, now more durable and more accurate
www.micasense.com
I personally like the Parrot Bluegrass complete package... the hardware and Pix4Field is useable on other platforms but for starters it puts it all on 1 support team.
That all said, I too looked at modifying several CGO3 cameras, gave that up quickly as I discovered more withn the Ag desired requirements. And... you can mount a Multispectral & light sensor on any platform including the H520 easily.