ABAP Query - SQ02 and SQ01 - custom selection criteria

Question

Hello
I am on 46C. In my infoset I need to define three custom fields for selections. I am able to do that. Once I create my query these appear on the selection screen. So far so good.
1. I need to use these custom selection fields as selection criteria for the tables in the join. How do I do that ?
2. If I need to default some values for these selection criteria, I can do that in the definition. However I need the values to be greyed out to prevent the user from editing the values entered. How do I do that ?
Thanks
Hari

Answer 1

1. I see that the standard variant assigned at the query level in SQ01. actually protects the selection field. There is no coding to make it only display. This answers part 2 of my question.
2. I am positive that the additional SELECTION that was created is being used in the main join that retrieves data in the query (in addition to being used for other things). I am not sure why somebody would define it that way instead of just creating a regular selection field in SQ01. Could it be because there is custom coding present for additional fields and there is reference to the selection variables needed for the additional field ?
How does one make this additional SELECTION also a criteria on the join ? I have attached the actual join Query generates - WRK, VKO and VTW are additional selection criteria.
FYI - this is an existing query, that I need to enhance
Thanks
Hari
SELECT MBEWBWKEY MBEWMATNR MBEWPEINH MBEWSTPRS MBEW~VERPR
       MBEWVPRSV MBEWZPLP1 MARAMATNR MARAMEINS MARA~MSTAE
       MARAMTART T001KBUKRS T001KBWKEY T001BUKRS T001~SPRAS
       T001WAERS MARCMATNR MARCMMSTA MARCPRCTR MARC~WERKS
       MVKEMATNR MVKEPRODH MVKEVKORG MVKEVMSTA MVKE~VTWEG
INTO (MBEW-BWKEY , MBEW-MATNR , MBEW-PEINH , MBEW-STPRS , MBEW-VERPR
     , MBEW-VPRSV , MBEW-ZPLP1 , MARA-MATNR , MARA-MEINS , MARA-MSTAE
     , MARA-MTART , T001K-BUKRS , T001K-BWKEY , T001-BUKRS , T001-SPRAS
     , T001-WAERS , MARC-MATNR , MARC-MMSTA , MARC-PRCTR , MARC-WERKS
     , MVKE-MATNR , MVKE-PRODH , MVKE-VKORG , MVKE-VMSTA , MVKE-VTWEG )
FROM ( MBEW
       INNER JOIN MARA
       ON MARAMATNR = MBEWMATNR
       INNER JOIN T001K
       ON T001KBWKEY = MBEWBWKEY
       INNER JOIN T001
       ON T001BUKRS = T001KBUKRS
       INNER JOIN MARC
       ON MARCMATNR = MBEWMATNR
       AND MARCWERKS = MBEWBWKEY
       INNER JOIN MVKE
       ON MVKEMATNR = MARAMATNR )
       WHERE MBEW~MATNR IN SP$00002
         AND MARA~MTART IN SP$00001
         AND MARC~WERKS IN WRK
         AND MVKE~VKORG IN VKO
         AND MVKE~VTWEG IN VTW
         AND MVKE~PRODH IN SP$00003.