For those of us that come from film to digital sensor based photography, sensor noise has always been an issue. The path to the best images possible has been:
1. Shoot at the lowest ISO possible.
2. Adjust your exposure so that your highlights are just below clipping (“expose to the right”), and adjust the resultant image to taste in post. This will push the noise, which is mostly in the dark part of the image down more into the black, where it is less noticeable.
3. Use noise reduction on that image.
4. Use stacking to average out the noise.
#1 will make the most difference, followed by the others in more or less the same order.
On substituting sensors it is not like changing film. Sensors are dynamic electronic devices requiring fairly complex real time sensor specific software to extract the photo site specific electronic voltages, and translate that voltage value stream into a RGB image. DJI hard codes this software into the drone. It will not work with any sensor other than the one it is written for.