There are most definitely people who customise many things on their boards, other gear, clothes, shoes and the like.
I guess the most common thing I have done is make popsicles into punk points for a while, when I couldn't get any more Black Label Jason Adams punk point decks.
Then more recently I have also rounded off the point on quite a few shaped boards for other people who didn't want a point, which is rather ironic with my own history, but I agree those boards did actually skate better with a more rounded blunt nose than a pointy one.
Others shave the sides off, or even cut down completely done bigger boards into more fun cruiser shapes or similar.
Also reminds me we used to get a lot of used decks, just cut a little off the nose if it was not worn at all, shape the worn down tail into a stubby nose and reuse them as "fun boards" for kids when we did skate lessons. Some of the kids liked them so much that we often ended up giving them the reshaped old boards when they didn't have a good one of their own too.
Some threads I know have shaped boards include the Cruiser thread, the Safe place for 7.75 boards and a couple of others, maybe shaped boards and something else threads too.