Yes it can be done.
You simply have to grind off both sides of the rivet (without damaging the inner ring).
Then carefully pry them apart.
I've done it twice and I wouldn't recommend it to anyone.
You can't generally use the outer ring because of chainline and most riveted and welded chainrings hace a pretty wimpy second ring (like 35-40T).
If you got the time, do the crime.