Quick fix

Did you ever launder a pair of slack to find that when you put them on again they were too short? Then when you go to take the hem down, there is a white line showing where the hem use to be? Well if they are black, you can try coloring in the line with a black sharpie. I would test it out on the inseam first and then do the rest.
The other option is after you take down the hem, center single fold bias tape, ribbon, or any other decorative trim over the line and stitch close to both top and bottom of the trim to secure in place.