title: How to change values on events of FM 'FREE_SELECTIONS_INIT'
body: <p>I created some dynamic select options. On my table, <strong>I want to have one parameter predefined and not changeable for the User</strong>. The not changeable I made with a callback form on the event:</p>
  
  <pre><code>data: LS_EVENTS type RSDSEVENTS,
      LT_EVENTS type standard table of RSDSEVENTS.
  
  LS_EVENTS-EVENT = 'O'. "at selection screen output §§§
  LS_EVENTS-PROG = SY-REPID.
  LS_EVENTS-FORM = 'AT_SELECTION_SCREEN_OUT'.
  append LS_EVENTS to LT_EVENTS.
  
  call function 'FREE_SELECTIONS_INIT'
   exporting
    KIND                     = 'F' "
  importing
    SELECTION_ID             = GV_SELECTION_ID
  tables
    TABLES_TAB               = GT_TABLE
    FIELDS_TAB               = GT_FIELDSTAB
    EVENTS                   = LT_EVENTS
  
  exceptions
   ...
    others                   = 20.
  </code></pre>
  
  <p>Now the callback form looks like this:</p>
  
  <pre><code>form AT_SELECTION_SCREEN_OUT tables
        LT_RSSELDYN "selections
        LT_RSFLDNUM. "dynpro info
  
    field-symbols &lt;FS_LINE&gt; type ANY.
    field-symbols &lt;FS_FIELD&gt; type ANY.
  
  
    read table LT_RSFLDNUM  assigning &lt;FS_LINE&gt; with key
    ('TABLENAME') = 'MyTab' ('FIELDNAME') = 'MyField' .
    if &lt;FS_LINE&gt; is assigned.
      assign component 'GROUP1' of structure &lt;FS_LINE&gt; to &lt;FS_FIELD&gt;.
      if &lt;FS_FIELD&gt; is assigned. "Group1 ausgelesen
        loop at screen.
          if SCREEN-GROUP1 = &lt;FS_FIELD&gt;.
            "Eingabe deaktiviert
            SCREEN-INPUT = '0'.
            "Ausblenden unnötiger Felder
            if SCREEN-GROUP3 = 'TOT'
               or SCREEN-GROUP3 = 'HGH'
               or SCREEN-GROUP3 = 'VPU'.
              SCREEN-INVISIBLE = 1.
            endif.
            modify screen."änderungen auf Screen speichern
          endif.
        endloop.
      endif.
    endif.
    unassign: &lt;FS_FIELD&gt;, &lt;FS_LINE&gt;.
  </code></pre>
  
  <p>That works. It sets the right values unchangable. In the first table, as the documentation says, the current values are saved. But if I change them, that does not work.</p>
  
  <pre><code>  read table LT_RSSELDYN  assigning &lt;FS_LINE&gt; with key
    ('TABLENAME') = 'MyTab' ('FIELDNAME') = 'MyField' .
    if &lt;FS_LINE&gt; is assigned.
      "&lt;&gt;-low = 'MyValue', &lt;&gt;-sign = 'I', &lt;&gt;-option = 'EQ'
      assign component 'LOW' of structure &lt;FS_LINE&gt; to &lt;FS_FIELD&gt;.
      if &lt;FS_FIELD&gt; is assigned.
        &lt;FS_FIELD&gt; = 'MyValue'.
      endif.
      unassign &lt;FS_FIELD&gt;.
  
      assign component 'SIGN' of structure &lt;FS_LINE&gt; to &lt;FS_FIELD&gt;.
      if &lt;FS_FIELD&gt; is assigned.
        &lt;FS_FIELD&gt; = 'I'.
      endif.
      unassign &lt;FS_FIELD&gt;.
  
      assign component 'OPTION' of structure &lt;FS_LINE&gt; to &lt;FS_FIELD&gt;.
      if &lt;FS_FIELD&gt; is assigned.
        &lt;FS_FIELD&gt; = 'EQ'.
      endif.
      unassign &lt;FS_FIELD&gt;. 
  
    endif.
    unassign: &lt;FS_FIELD&gt;, &lt;FS_LINE&gt;.
  
  endform.
  </code></pre>
  
  <p>Is there a possibility to restrict the change of those values? I just want them displayed in the Selectoptions if they are there.</p>