To be able to import read and write access into your user security of a model your import module should contain at least 2 dimensions: the user list and the list you're setting up security for.
Using a boolean formatted line item you can filter out the valid combinations on the intersections of those 2 lists. By filtering on that boolean line item you can create an import view.
The import view can be imported into the user settings part of the module, make sure you don't map the line item but map the list to the corresponding columns. The line item doesn't even have to be included in the view, it is only needed for filtering out the valid combinations.
Let me know if this helps,
Kind regards, Stef Jansen in de Wal Finext Performance Management