Yes, I've done it. I started by making a horizontal part slightly above the hairline @ the nape of the neck. Then I added a track in by stitching it onto the cap. Then I just repeated the same thing as I made my way up towards the crown of the wig.
I like the way it came out, but it still wasn't long enough for my taste. I was a loser & cut the length of the unit when I first received it.. & then later decided I wanted that length back so that's why I added tracks lol. I ended up just buying a new unit & promising myself to never cut it.
Adding the tracks was tedious for me.. but I've never worn a weave or sewed in a weave before, so the process was completely new for me.