Declare @MaxID int,
    @CurrID int,
    @SQL nvarchar(255),
    @Debug bit = 0;
Declare @DBs Table (DBID int identity(1, 1) primary key,
    SQLText nvarchar(255));

Set NoCount On;

Insert Into @DBs (SQLText)
Select N'ALTER AUTHORIZATION ON database::' + quotename(name) + N' To [sa];'
From sys.databases
Where owner_sid <> 0x01
And name Not In (N'master', N'model', N'tempdb', N'distribution');

Select @MaxID = MAX(DBID),
    @CurrID = 1
From @DBs;

While @CurrID <= @MaxID
  Begin
    Select @SQL = SQLText
    From @DBs
    Where DBID = @CurrID;

    If @Debug = 1
      Begin
        Print @SQL;
      End
    Else
      Begin
        Print 'Running command: ' + @SQL;
        Exec sp_executesql @SQL;
      End

    Set @CurrID = @CurrID + 1;
  End

Set NoCount Off;