[lammps-users] use lammps to chemical reaction systems

I know lammps can be used to chemical reaction systems(e.g. intramolecular cross-linking of BCB/styrene copolymers , Macromelecules,2009,42,8534-8542).
I can’t just add some bonds to the system directly and say that the reaction is completed. I need to let itself form new bonds.
How can I do it?

There is a fix bond/create command which will cross-link, but it is
for idealized (e.g. bead-spring) models. Adding cross-links to
all-atom polymer chains would require a new, more sophisticated
fix, e.g. to turn on angle and dihedral interactions when the bond
is formed.