You can harvest the top of the plant when she’s ready and reveg the bottom but you can’t reveg part of the plant and flower the rest at the same time.
If you want bigger buds all together you can reveg the whole plant and make her a monster but that’ll take a lot of space.
You can also do a perpetual harvest, when the top buds are done you can lower your lights a bit and keep the now exposed popcorn buds on to see if they’ll fatten. At the very least doing a perpetual harvest will allow the popcorn buds to finish up and mature.
Best of luck! 👩🌾🏼🌱