You can cast Serpent Sting under the effects of damage increasing modifiers (Exploit Weakness, Tricks of the Trade, Culling the Herd, etc) and have it keep those buffs so long as you never let that serpent sting fall off. This snapshotting only works with Damage Increasing modifers and not AP procs and things of that nature - as has always been the case.
The twist, however, is that Chimera-Serpent's damage isn't actually increased even if the Serpent Sting that's active on your target was a hugely buffed one. While this is of course incorrect behavior, it's largely made up for (and then some) by other positive bugs. The main implication of this is that it's probably not worth wasting a GCD to refresh Serpent Sting unless it's either very early into the fight, the damage increasing modifier on you is very powerful (think BQL's bite), or you're running with the 2p T9 bonus.