I picked up my p2000sk 357sig from the local hk armorer who was selling it to buy a new p2000sk 357sig LEM. He was selling because he did not know a way to change over to LEM. So either he is not a very good hk armorer or the answer is no.
The "decocker" on the P2000 V3 is actually the tail of the sear. When you press it you're tripping the sear. Since neither the Firing Pin Block, nor Catch move the pistol decocks rather than fires.
There are non-HK kits to convert P2000 V3 to LEM. Not sure if retaining the decocker is an option with them or not.