I've been thinking about this for a long time. Doing changes directly to the files on you computer via a webpage is really nasty, so that's out of the question.
But what I can maybe do, is allow you to upload a file or paste the entire content of a file into a field, and use this to read the current value. When you want to change your sensitivity, it can generate a new file you can download, or text you can paste into your file with the correct settings.