title: Disable a parameter input at selection screen
body: <p>I have screen filter at selection screen like this</p>
  
  <pre><code>SELECTION-SCREEN BEGIN OF BLOCK a WITH FRAME.
  PARAMETERS s_werks like resb-werks DEFAULT 'X' .
  
  SELECT-OPTIONS: s_aufnr FOR in_param-aufnr,
                  s_matnr FOR in_param-matnr,
                  s_bldat FOR in_param-bldat.
  SELECTION-SCREEN END OF BLOCK a.
  </code></pre>
  
  <p>and I want to disable just <code>s_werks</code> parameter but <code>SELECT-OPTIONS</code>.</p>
  
  <p>I want to disable it because it'll be exact value which is filled from table depends on the <code>sy-uname</code> :)</p>
  
  <p>How to achieve that?</p>