I learned bike repair working in a multi brand bike store in the 1970s. Cotter pins were a major part of the training since most of the cheaper bikes had them. I learned all the methods of removal/installation for Raleighs, french bikes, italian bikes and Japanese bikes.
Riding on loose cotter pins will ruin them. Causes gouges in the flat surface. Those should be replaced. And if you bugger up the threads removing them means replace the pins.
Cotter pins were made in different sizes. 8.5mm, 9mm, 9.5mm, etc. Italian bikes used thinner pins. Raleighs use the larger size.
The bike industry did make a variety of cotter pin presses. Var cast iron lever presses, BSA made a clone, Park Tool had a screw type similar to a c-clamp. Mark Stonich of the Twin Cities made and sold a batch of them about 15-20 years ago. Bike Smith has some for sale
https://www.bikesmithdesign.com/CotterPress/The VAR is made of cast iron and we learned the hard way you never use a hammer on one.
A hammer and punch works if the crank is well supported and your aim is excellent. Regular C clamps have too course of threads to get the necessary force. if you make your own, fine thread bolts will allow you to to get more pressure on the pin.
here is a vid on making a cheap press
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