Updating commercial extension

Question

I'm about to deploy a commercial extension but have some doubts relating to updates.
My scenario is a couple of extensions which should be installed at same time and a lot of resource files to be installed in the users Documents folder.
So far no problem, I add the second extension to the first in the manifest, create an hybrid extension and add the resources folder with destination "Documents".
I belive I only need to sign the extension package, later I double click at the mxi file to allow extension manager to create the big zxp file which doesn't need to be signed, correct ? ( Seems to work)
Ok, the problem now is that I need to control which users may update and which not, adding an automatic update in the mxi file means no control, therefore I guess I have to send the new version zxp manually but then Extension Manager requests to uninstall the old version which means deleting the resources folder.
I need a way to update the extension without affecting the current resources, may be adding more but not deleting the current ones.
It would be great if the extension itself could download and install the update like I do with additional resources instead of the Extension Manager who doesn't know about the user.
I have tried to add the update in the mxi file but this way I must include all resources again in the update or they will be deleted automatically by the extension manager.
Thanks for any help

Answer 1

It is possible to mark a file as a "system file" in your MXI file (see http://help.adobe.com/en_US/extensionmanager/cs/using/MXI_tech_note.pdf). I believe that will prevent it from being removed on uninstall:
<files>
     <file source="myResourceFolder" destination="$userhomefolder/myPlugin" systemfile="true" />
</files>
That should avoid your resources being removed when you update. If you want to add new resources in your update you'll need to make sure the destination for any new files is within the resources folder that you initially created. If you just had a new resources folder that you installed to the same location then I think it will overwrite the original resources folder (rather than, say, merging them).
<files>
     <file source="myResourceFolder/additionalFile.txt" destination="$userhomefolder/myPlugin/myResourceFolder" systemfile="true" />
</files>
Hope that helps,
Louis