I haven't seen "square" areolas. It's probably just scarring, some get thick, some stretch and distort a little. Cis men have varied nipple and areolas too. My dads areolas are very small, like nickle size, my brother on the other hand has silver dollar size areolas.
The way they change it depends on the surgery type. If you have DI with nipple grafts, they cut a small circle of your areola and a small one of your nipple, sew them together and graft them to your chest. Peri and similar procedures they cut slivers from the edge of your areola, as far as I know.