To create this look, we will need to have two different iterations of the same seam to apply to either side. We can begin by cloning our existing seam:
Then, open the diffuse map of the original seam and crop it to only include the top half of the image:
With the image editor still open, we will reflect the seam over the X and Y axis. Select the hamburger drop down in the top right corner, and select "Flip Horizontal" and then "Flip Vertical":
Next, open the seam we cloned earlier. Crop this image to only include the bottom half of the seam:
No additional adjustments are needed to this seam.
Now, apply one seam to each edge:
Note: you may need to adjust which seam is applied to which edge. If you notice the seam is upside down when you apply it, try applying to the other edge instead.
Last, use the texture tool to align the two seams along your edge. It can be helpful to have the 3D and 2D windows open at the same time while doing this. Use the 3D window to check alignment, and use the 2D window to select the edge which you are moving.
Tip: with the texture tool selected, you will know you are adjusting a seam texture when the edge turns green:
You may want to set your stitch construction to flat to avoid any bumps in-between your seam:
You've now created a seam that covers two edges!