There are multiple possible causes for fouled plugs. I can't say the seafoam will fix it… But it shouldn't hurt it. But if it is happening in all cylinders, I don't think it's a sticky piston ring. What are the chances of that happening on every single cylinder? Try it but don't be disappointedif it doesn't fix it.
As for what is involved in replacing piston rings… it is a VERY involved process which includes pulling the motor out and tearing it down. Not impossible for the average person, but very time consuming, and things can easily go sideways. Look up a few videos on YouTube. You'll get the idea of how to do it. If you DO tear into it yourself I recommend photographing everything before taking it apart. Take a pic, take off what you photographed. Take another pic, another part. Etc. So that you can go back and see ‘ah HA! That's how that goes there!
'''Worn or damaged valve guides or valve guide seals.''' Problems here can allow oil to dribble down the valve stems and enter the combustion chamber. Oil will form heavy black wet oily deposits on the spark plugs.
'''Worn or damaged piston rings, or worn or damaged engine cylinders'''. Badly worn piston rings, broken or cracked piston rings, grooves or scoring in the cylinder walls, or even piston rings that have been installed upside down can allow oil to get into the combustion chamber and foul the spark plugs.
'''Rich fuel mixture.''' This will produce black fluffy deposits on the spark plugs. If only one or two spark plugs are affected, the underlying cause may be a leaky fuel injector. If all of the spark plugs show heavy dry carbon fouling, the rich fuel mixture may be caused by too much fuel pressure (check for a defective fuel pressure regulator or a plugged fuel return line). A defective oxygen sensor that reads lean all the time can also make the fuel mixture run rich. Check fuel trim readings with a scan tool to see if the engine is running rich (negative fuel trim numbers that are -8 to -10 or more would tell you the engine is running rich). On an older carbureted engine, a rich fuel mixture can be caused by a leaky float, incorrect float setting inside the fuel bowl, a leaky fuel inlet needle valve, or incorrect jetting (too large).
'''Leaky Head Gasket'''. This is really bad news because a leaky head gasket can be very expensive to repair. If coolant seeps into the combustion chamber, it will form fouling deposits on the spark plug. A fouled spark plug may be an early sign that a head gasket is starting to leak.