Heterogeneous nucleation of a FeMnCrCoHigh Entropy Alloy

Iam doing the solidification of a high entropy alloy.I have heated the system to 2300k and cooled it to room temperature.I have found crystallization at 1000k this is for homogeneous nucleation.Now iam trying to do heterogeneous nucleation for which iam taking the dump file at 1200k and then i want to make the positions of few atoms at the center to fcc so that it acts as the fcc seed for heterogeneous nucleation.So i need few suggestions as to how do i make 444atoms at the center of a simulation box of size 101010 to fcc structure
Thanking you

A couple of suggestions:

a) you can do this yourself as a pre-processing
step for a new LAMMPS run. Convert the dump
file to a data file (LAMMPS can do that if you
use read_dump and write_data). Manually delete
a few atoms from the data file or change their coords
to be the fcc center you want. Then read the
new data file into LAMMPS.

b) convert the dump file to a data file, read it into
LAMMPS. Use the delete_atoms command to
remove a center chunk of atoms. Use the lattice and
create_atoms command with a small region in the
center of your box to create the new fcc lattice region.
You can use delete_atoms overlap in case you created
new atoms that are too close to old atoms.