well hmmm you could test it if you like. Take out all the fuses for all your electrics. Swap the negative and positive terminals. See if your car rusts
I could well be wrong but I just can't see how it could be any different. If I swap the terminals at the battery the electrons will now be flowing from the chassis into the battery rather than from the battery into the chassis.
Either way no difference. I could move my ground point or move the battery to the boot and change the direction the electrons flow.
Maybe I've missed something but + and - only seem to be descriptors.... why can I touch a negative cable but not a positive one? Simply because I might become a link to another negative surface. But if it was all the other way around, now could touch the positive but not the negative.
Until proven wrong I don't see how electrically anything has changed. It's like swapping poles on an AC current - absolutely no difference.