If the Defending Pokemon is already Asleep & Poisoned with a condition that places more than one damage counter in between turns, can you use Hypnotoxic Laser to change the number of counters to be placed?
Yes, the new single-counter Poison condition replaces the multi-counter Poison condition.
Source: TPCi Rules Team (2013-02-21)

Relevant cards

Note: All applicable cards may not be listed below.
BW8_123