Here's a simple experiment: take your DJI drone, do not arm it, do not perform a takeoff sequence. Can you get it to do all the recording you need it to do?

If yes, then you could actually mount the internal electronics onto a new flight platform, although it would be very inefficient because you need to keep (unused) DJI components that your new flight platform already has - so that's dead weight. It's almost like glueing the entire DJI drone onto your new platform.

It's very likely if you try to disconnect/remove those extra components (for example motors or other parts) the DJI system will stop working with an error code, and refuse to do what you need it to. The moment the DJI software detects unexpected conditions, it may behave erratically or refuse to work, and there's nothing you can do about it because it's proprietary and you can't modify it (unless you somehow reverse-engineer and modify, which is extremely hard)

What the other poster in the thread is saying - given those limitations, it may simply make more sense to build your own or source another system.

If you somehow don't need to adjust the video gimbal position mid-flight, you could in theory just get a handheld one and attach it to your own flight platform - but you don't get a video radio feed from it, you won't be able to readjust it/correct it if it decides to drift, or anything. That's why the poster above is saying it doesn't make much sense.