Make it easier to handle the options of selecting specific files for a subsequent operation.

Provide three buttons, whose use would be determined by the default selection you provide the user.

If all are checked initially, and the user only wants to operate on a few, he could uncheck the ones he wants and then user the invert selection.

If none are checked initially, and the user wanted to operate on a few, he could check those and then use the invert selection.

Various combinations of these buttons could be used depending the initial default selection to make the overall process simpler.