It's difficult to unravel from the bottom. And yes, your stitches will look upside down. How noticibly so depends on the pattern.
However, you can learn to kitchener stitch!
Cast on with fresh yarn in the color of the stripe you are replacing. Knit it to the size of what you want to replace. Leave it on the needle.
Use the other needle to slide it through the stitches of the lowest row of the scarf that you want to keep.
Then kitchener the two pieces together . See video
Once you are happy with the grafting, carefully snip away the original stripe, one row lower than the grafting row
Unpick the last row and weave some of it in as a tail.