I don't know the answer but have to ask. If you have the camera & the software why not take the same photo in both settings & see how the 2 RAW files look when opened? If they are different see if there is a menu option which allows the modified aspect ratio to be returned to a normal 3:2 ratio.
I think it depends on the camera and the raw processor.
At least on a 7D Mk II, all you have to do is open the RAW file in DPP and use the crop and rotation tool to set the aspect ratio back to what you want. (I know because last summer my wife accidentally shot a series of pictures on her 7D2 with an erroneous aspect ratio setting. Fixing it was tedious but simple.) If you were shooting in JPEG, I suspect that you're stuck with whatever was set.
Let's say you took a picture in 16:9. If you shoot in RAW it's always saved with a little more data in 3:2.
My question is: If you took a photo in RAW in one aspect ratio, is there a way to revert it back to 3:2 since the information is there?
If you saved the images as RAW, then there really isn't any one aspect ratio, aside from the properties of the original image that was captured from the image sensor. In other words, your post processing software should be able to crop the original image to any size, or ratio, that you want.