If the a/c has a cable connector for 120, can I change the cable to convert to 115 volts and connect it into a regular switch outlet?

The problem is not the voltage. No need to convert. Equipment that functions on 120 also functions on 110 and 115.
What may be a problem here is the current draw. An AC has a power capacity of around 2.5 Kilowatt, which means at 120-115-110 around 23 amps.
I am not sure if a regular US switch outlet (and it's corresponding fuse on the mains-panel) can handle that current.

Success !