I created the Substitution already, but its not updating COBL field (wbs element).
I am able to update BSEG fields through substitution.
following code I am using...
ASSIGN ('(SAPMF05A)COBL') TO <fs_cobl>.
IF <fs_cobl> IS ASSIGNED.
<fs_cobl>-ps_psp_pnr = lv_psp_pnr.
<fs_cobl>-ps_posid = 'P00851300002060000'.
<fs_cobl>-objnr_real = 'PR00087131'.
<fs_cobl>-co_kapro = '1'.
<fs_cobl>-xauto = 'X'.
<fs_cobl>-KTOSL = 'KDF'.
ENDIF.