You need to synthesize the silver nanowires by controlling nucleation and growth mechanisms during synthesis afresh and not from silver nanopowder already obtained.
Put these particles on silver substrate, moisten well with silver salt solution or dip the whole NP paste-plate assembly into silver salt solution. Now electrolyze, keeping the the NP-subsrate plate as cathode. do not stir. wait for a while, and you would see silver dendrites growing. So, some nanoparticles would indeed turn into nano-rods or nano-forks, I guess.
Or you might dissove some NP with conc. HNO3 and try to redeposit same way.
Or completely dissove this NP mass into oxidizing acid, and synthesize nanorods from there!
By applied external electric field you can polarized these nanoparticles. After their polarization you can manipulate them by application external electric fields because the dipole of such nanoparticle will be oriented according to rule; "The field of polarized dipole should compensate the external electric field". Accordingly, the nanoparticle dipole will be reoriented on the substrate of iside the solution.
I applied different voltages, but each time the absorption peak corresponding to silver nanoparticles gradually decreased with increasing voltage and increasing time.