Can you run 4ohm resistor to make 4 ohms speakers 2 ohm?

Yes, you can safely use a 4 ohm amp with one 8 ohm speaker, but you will not achieve full power.

The 4 ohm amp is designed to supply a certain voltage into a 4 ohm speaker. Supplying that same voltage to an 8 ohm speaker will result in half the power, or -3dB. For maximum power, use a 4 ohm speaker, or two 8 ohm speakers in parallel.