(no subject)

I have two polymerchains consisting of 100 monomers each and I have FENE bonds between the monomers. I want to truncate and shift the lj potential for dispersive interactions between the monomers,so that each and every monomer also interact with each other through the shifted non-bonded potential. Does a bond_fene/expand command do that or will I have to use separate pair_lj/shift command?

The bond style only sets how 2 atoms wiith a bond bewteen
them interact. The pair style is for other 2-body interactions

(i.e. between atoms that are not bonded). You can look at
pair lj/cut and pair_modify to see the formulas and shifting options.