Most of my unis have at least one part swapped out on them. Different length cranks, some new pinned pedals if it didn’t already have a set, maybe an aluminum seat post if it previously had a steel one, stuff like that 
I would highly recommend learning to build wheels if you haven’t already done so. The wheel for me is the “centerpiece” of the unicycle, so on my more involved projects I like building up a nice wheel. For example, on my first project uni (A CyclePro 20”) I disassembled the wheel so I could do a good job at removing the rust, then when I put the wheel back together I used purple spoke nipples which gave it a nice personalized look. I did something similar when I built a freewheeling 650b wheel, but this time I did alternating purple and yellow spoke nipples. You can do a lot of customization with wheel build if you so choose, spoke nipple colors are just scratching the surface.