MTR - Airport Express Travel Pass

I will be at Hong Kong from 3/4/13 to 8/4/13, if I purchase Airport Express Travel Pass, 2 designated journey(s) on the Airport Express and any 3 consecutive days of unlimited travel at HK$300 on the MTR, the Light Rail and Bus who have been in Hong Kong for less than 14 days at the time of purchase. Can I use the same card to top up for day 4 to day 6, if yes, how to top up in more economical way.