From personal experience, my piercings haven't shifted with HRT-induced breast growth. Even when the subareolar disk was developing, it never pushed out or shifted my piercings. And replacing jewelry/up-sizing isn't really an issue...it's kind of fun actually...just like shopping for anything else (but again, wait till you're fully healed before shopping for pretty or ornate jewelry...a simple hoop is - IMO - the best to start with).
Is a sports bra a compressive garment? Maybe, but I never had issues using them...maybe I just lucked out? In any case, one trick I use(d) is I'll stick a regular rectangular band-aid over the piercing if I'm wearing a sports bra/compressive...even though the garments would be tight, the band-aid would make them slide over the piercing. Don't use one of those small round disks - those aren't big enough to securely fasten over the piercing and will fall off. The band-aid also helps keep the ring flat and not twist around (and at the end of your activity, you could check the band-aid to see if you bled or leaked anything [which you could still differentiate from sweat]). The band-aid trick has served me well when I go cycling - typical kit will be sports bra, bibshorts (which have shoulder straps that inconveniently slice across the boobage) and then tight fitting cycling jersey...no issues for me...as long as I slip a band-aid on. YMMV.