Is there a way to modify the exposure on a specific part of an image using rawtherapee, Gimp's ufraw, or any other free/open source tool?
I'm doing it my way in GIMP - I take "Free select tool", select the part I want to modify. Then I feather the edges of the selection by 30-100px depending on the size of selection (most often I go for 50px), then I copy the feathered selection and past it as a new layer. This way I can do any adjustments to this particular bit and the rest of the image will remain untouched.
It takes time to post process an image this way, but it allows me to achieve desired results, so I like to work like this.