[Jasim]

Plugin mode is a bit different to standalone. Standalone mode allows you to save sessions, whereas as a plugin it only operates on the selected layer image and doesn't save any other information. If you think you might want to re-edit an image, it's probably best to edit in standalone mode and save the session.

The lighten /darken tools will not selectively affect the stretch marks. However, there are also brushes for smoothing skin and removing blemishes that may be useful. Tummy tuck is a slider in the skin section, above the belly button replacement and below smooth skin.