Yes. You check if each one of of the four fields YB01-YB04 is set to X. If yes, then you modify the only row in the table IT using the field symbol.
so you should have something like this inside the loop.
read table temp with key user = <fs>-user
yb01 = 'X'.
if sy-subrc is initial.
<fs>-yb01 = 'X'.
endif.
read table temp with key user = <fs>-user
yb02 = 'X'.
if sy-subrc is initial.
<fs>-yb02 = 'X'.
endif.
read table temp with key user = <fs>-user
yb03 = 'X'.
if sy-subrc is initial.
<fs>-yb03 = 'X'.
endif.
read table temp with key user = <fs>-user
yb04 = 'X'.
if sy-subrc is initial.
<fs>-yb04 = 'X'.
endif.
V.