You can buy rubber inserts of the right size that can be installed and then tighten with a wrench or socket to seal the hole.
Google: rubber expansion plugs automotive
"freeze" plugs are located in the block only so below the exhaust and intake manifolds, there are also some on the back of the engine inside the bell housing.
No, "freeze" plugs don't effect engine performance, overheating with the loss coolant would be the result of a leaking "freeze" plug, but engine would run fine ....until it melted

.
Knocking could be an exhaust leak, or worst case a bad connecting rod for a piston.
"freeze" plugs are not there for freezing, they are there to close the holes left when the casting of the block was finished, it's how they get the sand out.
Proper name is Core plugs, but everyone calls them freeze plugs or expansion plugs, so why rock the boat, lol.