determine statically if a LOOP is active over "Ztable"

I am trying to avoid loop to update a table.

 loop at lt_ztable assigning <lf_zme_prepa_usr> . 
<lf_zme_prepa_usr>-bname = ls_record-new_username.
 endloop.

*how I used to modify the internal table

 ls_ztable-bname = ls_record-new_username.
 modify lt_ztable from ls_ztable transporting bname .

When I run the code inspector:

In the table "LT_Ztable" a row was to be changed, deleted or inserted. It is not possible to determine statically if a LOOP is active over "LT_Ztable"

Is it okay to modify an internal table like this and more importantly is it more performant than the field symbol?