I would probably start by adding a button to the ribbon instead of modifying the Tridion Edit view with a checkbox.
Then, when clicking the button, you would need to be able to grab the checkboxes in the form with Javascript / jQuery. This part could take anywhere from a few hours to days, depending on your luck with Selectors and skill with JavaScript. This kind of code is very specific to the Edit window you have open in Tridion.
It is also possible that in a future version of Tridion the HTML could change and your extension would need to be updated. I would suggest to compare the HTML from 2011 to 2013 for this view. I am guessing it is not changing too much. This would then give your extension a good 2-3 years, if not more, before there would be any risk of it needing to be updated.