GOT IT!!!
Finally got it right...Here it is if anyone is interested
Function ChangeQueryDef() As Boolean
Dim stdocname As String
stdocname = "exsisting query"
'open exsisting query in design mode
DoCmd.OpenQuery stdocname, acViewDesign, acEdit
Dim strQuery As String
Dim strSQL As String
strQuery = "exsisting query"
Dim dbs As Database, qdf As QueryDef
Dim Or1 As String
Dim Itemid1 As String
Dim xxx As String
Dim yyy As String
xxx = [Forms]![frm OracleBOM AllReport]![OrgNo]
yyy = "233344"
Set dbs = CurrentDb
strSQL = " New Query pasted in design mode ex select
OR1, Itemid1"
strSQL = Replace(strSQL, "OR1", (xxx)) 'make changes
strSQL = Replace(strSQL, "Itemid1", (yyy))
Set qdf = CurrentDb.QueryDefs(strQuery)
qdf.SQL = strSQL
qdf.Close
RefreshDatabaseWindow
ChangeQueryDef = True
End Function
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