I always forget that they can be customized and because of that, no I don't customize them. But that's because I always forget that I can tbh. Even if I do remember, I usually sell any gyroids that I find lying around so I don't think I'll be changing them up anytime soon. Ontop of that I prefer to keep things that can be customized as their "default" as it feels like they were intentionally meant to be like that, so I try not to mess with things too much. I think if I were to though, i'd put too much time into picking and choosing my gyroids rather than running the actual town.
I've never changed the gyroids on the stage even though I knew you could, I've just never really been that interested. I might in the future when I'm done landscaping my town but I'm dealing with a lot like that right now lol. So I don't know when that'd be
I've had New Leaf since it was released and I didn't know you could change them until about a year ago lol. But no I haven't changed them because I don't really care about gyroids too much and I haven't found any that I like enough to go and switch them. I do like the idea of putting brewster gyroids there though, they're just taking up space in my dresser lol