HI Priti,
1. We cannot give any authorization on data which is been viewed in dashboard in your case as data is been picked up from Excel. You can give authorization on data that is shown in dashboard if your data is coming from BW system to reporting side but for Excel is not possible.
2. Since the User's login through the Launch pad to view the Dashboard it is safe to give only .SWF file as it runs on browser which does not require Xcelsius Software and if you give the user XLF file there might be a mismatch of mapping if He/She moves around the canvas.
3.Anyhow you are using Launch pad so developing a Webi Report will solve your issue. On top of Excel Sheet create a Webi Report with the blocks that are required as part of Dashboard Requirement and place Excel and Webi Report in the same location(For Easy of Use), now import the data from Report to Excel(Spreadsheet of XLF file) through Live Office(Excel Addin) or WebService and develop Dashboard on top of it and place the .swf file in the required folder.
4. For Auto update of data in Dashboard you need to just update the Data in Excel sheet which inturn updates the webi report. You can schedule the Webi Report for a required frequency. Select the properties of a Data object in Excel as "Pick up the Latest Instance" if you are going through the Scheduling concept if not you can proceed with the Use Report Saved Data(Draw Back is you need to refresh the report and save it :: This is not useful in your requirement) or you can go with the
"Refresh On Demand" in which user will be prompted to specify the selected criteria which in turn will return the latest data.(This would be very useful in your case as no need to schedule the reports and refresh the reports). Every time the user will be able to see the latest data.
Hope this may help you
Regards,
G.SaiNath.