There are several things to consider with this. It might be different with different piercers, but for me whenever I've gotten a new piercing I had to leave it in 24/7 for a full year before I could take it out and put it in later on again. With any surgery, you most likely can't have any piercings in while under anesthesia, cause of infection risk and what not. And that goes for all kinds of jewellery.
Then it's what others said already as well: if you'll get your nipples re-sized you most likely can't put a piercing jewellery back in them again after surgery. So you'd have to get them re-pierced then.
As for getting them pierced after surgery, there is no guarantee it will work if they're scarred after re-sizing, but I have heard of several post-op trans guys who have been able to with no issue. Chase Ross on youtube did, for example, and he vlogged about it too, so you can search for that on his channel on youtube if that's of interest. Those videos are about 1-1,5 year old.
I want to get one of my nipples pierced if I can, and I've had my top surgery 4 years ago. But I'm gonna get bottom surgery relatively soon and because I know I'll have to take out all piercings/jewellery for op, I'm waiting until after surgery.
And then a last point: you're gonna have to wait quite some time after top op to get the nipples pierced, cause they need to be fully healed. I think at least a few months, but a piercer would know that better.
In conclusion: it's better to wait until after surgery, cause you likely would have to re-do it after anyway then.