If the swaged end is not rolled over very much....i.e., barely flared...you can usually crush it with a pair of needle-nose pliers sufficiently to push the rivet through to a point where....
You can get a sprue-cutting type of pliers under the rivet head, and pry the rivet out. Or cut the head off and drive the remaining portion back thru with an appropriate sized nail or old drill bit. This is my preferred technique if there's enough room to get the cutting pliers under the head in the first place: Cut off the head, you're home free.
Which leads to the 'postmortem' recommendation...don't flare the new rivet any more than necessary to keep it from freely backing out of the knuckle hole. If you leave enough axial play in the rivet, getting the sprue-cutting plier jaws under the head is the quickest way to a future repair......IMHO, of course.
This is like the sprue-cutting plier I use....
I use an old one....cutting edge a tad ragged. DO NOT use a sprue cutter that you intend to use for cutting plastic sprues. You don't want to compromise that tool used for a single purpose. Use an old cutter....mine came in a collection of tools from an estate sale. The coupler knuckle rivets are really quite soft....blackened brass, I believe. An old cutter is just the thing for getting under the rivet head.
Works for me, anyhow.