I think going back from departure level to arrival level should still be possible, but needs some tricks that's been discussed in the forum before.
while for The Arrival lounge, the access criteria have been adjusted slightly a month or two ago, and now if your transit in HKG is more than 4 hours, you can access The Arrival too...
Extending access of The Arrival at Hong Kong International Airport
In response to feedback by passengers, with effect from 1 February 2009, the new admission policy to the lounge is for the day of arrival and is extended to First Class passengers, Gold and Diamond members of The Marco Polo Club, and Emerald members of oneworldŽ, arriving on flights operated by Cathay Pacific or Dragonair to Hong Kong as final destination, or transiting to other destinations with more than four hours of transit time in Hong Kong.