Is it OK to apply too many volts to Actobotics HD motors?

Like jsotola said, the datasheet will tell you how much voltage is too much. Regarding damage, the higher voltage can cause too much current in the motor windings and potentially melt the insulation off, shorting the motor internally, or it can overspeed the motor and cause bearing damage.

I know it doesn't sound like a big difference, but 14.8 V is almost 25% more voltage than 12 V.