when playing a command cards, such as covering fire, that have a certain requirement can they still be played without meeting, such as using covering fire with only two corp units in range instead of 3.

Yup! The text you’re referring to is not a requirement. It’s the specific units you get to issue orders to at the start of that round.

The only requirement (that I know of) are that if the command card is specific to a named commander or operative, that unit must be selected to issue the order.