Most kayaks have something custom going already wether it is outfitting or stickers (even paint).
You may have a real challege doing custom parts because most boats specs are slightly different. A JK grab loop will not fit on a LL, WS, or Pyranha and so on.
Squirtboats are all one off. If you really want to have a rad one off boat. Go Glass!
I do have a friend that added little pink pompoms to his EZ. If flair is what you're looking for... search an eddy and you'll find something to glue onto your boat. Still I think boaters are cheap and you will lose money building something that people can do themselves. Start simple and don't spend a lot of your own money.
I love to dance, but who needs the music- It throws me off.