perl -i -pe 's/\.mbh_succ_roam_i_vlr_e_plmn/\.new_mbh_succ_roam_i_vlr_e_plmn/g' <input_file>

##</code><code>##

file content,
__DATA__
.mbh_succ_roam_i_vlr_e_plmn   next
.mbh_succ_roam_i_vlr_e_plmn1  first
.mbh_succ_roam_i_vlr_e_plmn2  verify