Can you use a 5v 1A charger for a 5v 500mA device?

No. In general, a charger needs to be able to figure out when the battery has reached full charge, otherwise the charger can damage the battery by overcharging it. You need to use the specific charger required for the battery.

And, if you are trying to power a non-battery device that requires 1A from a 5V 100mA source, you will not be able to maintain 5V, so it will not work there either.