If you have a black spring, you have the 14-lb Heavy LEM spring. A 12-lb spring would be a Blue-color spring and I believe HK is still shipping them in Blue.
What I would suggest is shoot the gun as is for a couple of hundred rounds, getting used to the light trigger pull. Then swap the light TRS with the medium TRS that came with the V4.1 LEM kit, shoot a few more, and see which pull weight you would prefer because if you didn't and found out after the fact that the medium TRS was too heavy for your taste, it would be another trip to the armorer to have it swapped out. The reason is when the armorer replaced the stock Trigger Bar Detent Spring (TBDS) with the V4.1 TBDS, he would have to replace the stock TRS as well, and if you don't like the medium TRS, he would have to put back the stock TRS and TBDS. The TBDS would require a complete removal of the hammer group while the TRS could be easily done with the HKParts's TRS Pliers.
I have a tutorial in the Reference Library and you could try it yourself. Why not, right?
ETA: Forgot to mention that the gun can be shipped directly back to you and not your FFL.