I actually have both nipples pierced - both were in for years before starting HRT. I've not noticed any negative changes or movement to the piercings, even though I'm going through breast development. Unless the piercer really goes deep into the areola, I don't see an issue. Mine were pierced in my male-phase - even with the right nipple pierced deeper than the left (right at the base of the nipple/top of the areolar junction), I've not had issues. I can feel the glandular disc just enough below the piercing.
I guess it also depends if you're nipples/areola will actually widen out while on HRT - mine haven't, so I've not needed to place wider rings. Growing nipples shouldn't really be a big deal, though...I mean, well-endowed women have been getting nip pierced for a while, so I don't really see any difference or issue if you need to keep switching out, plus, it will give you a reason to try new designs, metals, or colors. Mine are simple titanium 14g full hoops.
I love my piercings - evidently so does everyone else who's been lucky enough to find out...