Will overfilling engine oil have any effect on the catalytic converter?

Your biggest problem with overfilling the engine is not damage to the converter but damage to the engine itself. Overfilling causes the crankshaft to make contact with the oil. This will cause a situation where air will be mixed with the oil. This air mixed with the oil causes the oil to lose it's lubricating properties as air is a poor lubricant. This will cause the engine to overheat and will result in severe wear to all moving parts within the engine. If you overfill the engine drain the excess oil out immediately.