I'm not sure what you are calling a 150 watt pack.
The answer is, no you cannot plug a MH bulb into an HPS setup.
The answer is, you can modify the HPS setup to be able to burn MH if you are handy with electric.
The other answer is that 150 watt MH bulbs aren't very plentiful, the standard bulbs are 175 watts, for this reason you would probably want to buy a 250 watt HPS setup, modify it and then run either HPS or MH bulbs. Or even move up to a 400 watt.