An added bulk action would be ideal for this. Unfortunately it’s currently not possible to add custom bulk actions.
Thus it appears some sort of jQuery/AJAX application would be necessary. jQuery to insert a button and identify the posts checked, AJAX to have the server make the changes and send back to jQuery the changes that were successful. jQuery can then update the appropriate HTML, or simply force a page reload.
Considering one can make similar changes manually rather quickly by using the Quick Edit feature, albeit one post at a time, consider carefully if this is worth your development time. Especially considering your script actions are limited to the posts currently listed on the page, 20 posts max. per page.
User interfaces take a lot of coding effort. If this is for a one off task to not be repeated or repeated infrequently, a utility script with no user interface could be built relatively quickly. The crux would be how the script determines which posts to change and which to leave with no user input.
