I guess it'd be considered a body mod.
I've barely got enough in the chest area to even be considered female because I'm awkwardly skinny (22-year-old woman with the build of a 12-year-old boy, really) but I've never been self-conscious about having small breasts. I go jogging and sleep on my tummy with no issues!
Also, I found that healing my nipple piercings was a
lot easier than my friend who got hers done at the same time and has large breasts. I love my piercings more than I'd love a big pair of boobs... I mean, they're for feeding babies. Other than that, I never understood the aesthetic appeal?