Currently, there is no public extension in SAMSON that can launch/use LAMMPS. But you can export your system into a LAMMPS Data format and load LAMMPS files (data and trajectories) back in SAMSON.
We plan on adding the support for periodic boundary conditions in one of the future releases of SAMSON. For some systems, you can simulate without PBC or by freezing the boundary atoms to fix them.
You can also combine simulations in SAMSON with e.g. ASE package using Python, see Python scripting: Combining SAMSON simulation with ASE calculators