The acorn nut is tightened by the expanding end of the rivet as the rivet is installed. It is likely that removing the acorn nut by prying would remove the tension of the rivet, since the rivet may have expanded and snapped up to 1/4" before actually contacting the surface that the acorn nut was resting on, since it snapped when the rivet could no longer expand within the acorn nut.
I would prepare to replace any removed acorn nuts with either a new rivet, or do what I have done and replace any broken rivets with 1/4 x 20 stainless steel screws and nylock nuts. Pro Dec company sells snap cap washers specifically designed for the 1/4" stainless steel screws, and many other sizes also.
We have had a couple acorn nuts just fall
off over time, which we replaced with the SS screws.