Can a 220V relay be used to switch 110V appliances?

The 220 volt relay could be used to switch 110 volts. However the contact current rating will not increase. Contacts rated for 5 amperes will not be safe switching more than that, certainly not 10 amperes. The contacts carry the current when closed so the voltage is not the issue but the size and material of the contacts is important. Therefore do not exceed the contact current rating no matter what the value of the voltage being switched

220 V(AC), 5 A Relay means, you can switch upto 220 V, safely across the relay and 5A is the maximum current allowed to flow through it. Current rating remains the same, even if you are switching 110 V.

Exceeding the voltage rating may cause the insulation to pierce while exceeding the intensity (for a long enough time) will cause the conductors to overheat. Lower voltage but higher amperage means the same power, but the dissipated power may be larger (experiment required), hence risk of overheating.

If this is a professional work, you will likely breach the code for exceeding the allowed Amp value, and you will be hold liable if something bad (like a fire) happens. If this is a lab setting, test before using, it may work.

The relay rating is for max voltage and amps, using lower voltages and amps is OK.