You need an implicit enhancement and the end of the method BUILD_DROP_DOWN in class CL_XSS_CAT_APPR_RFC_CMD_TOOLS.
ENHANCEMENT 1 ZENH_CAT_APPR_BUILD_DROPDOWN. "active version
read table xt_fieldlist ASSIGNING <ls_fieldlist> with key tec_name = 'DD_APPROVE'.
check sy-subrc = 0.
read table lt_f4_value into ls_f4_value with key value = if_mss_cat_appr_bl_constants=>gc_keep.
check sy-subrc = 0.
IF iv_view = gc_drill_down.
ls_f4_value-text = text-003.
ELSEIF iv_view = gc_single_item.
ls_f4_value-text = text-007.
endif.
delete lt_f4_value where value = if_mss_cat_appr_bl_constants=>gc_keep.
insert ls_f4_value into lt_f4_value index 1.
<ls_fieldlist>-f4_values = lt_f4_value.
ENDENHANCEMENT.