I strongly suspect there's creaking coming from my pressfit BB on a road bike.
What I don't know is whether the pressfit BBs is reuseable, so once I remove and regrease the whole thing in there, can I use the same BB again and put it in?
Unlikely that the creak is in the bearings themselves due to needing re-greasing. It's probably at the press fit interface between the outer race and the frame.
Yes you can remove and refit the bearing units. If the BB shell is metal you can use grease or retaining compound to try to stop the creak.
Global Cycling network did a video on BB creak recently.
It's possible but dubiously worthwhile and not common practice. If you want to do this you have to be careful that you're removing them in a way where you're not putting any pressure on the bearings themselves, because this can cause damage, and also not damaging the cup with the tool. The purpose-made tools for this task (i.e. Park BBT-90.3) can be kind of hit or miss at accomplishing all this. All these bottom brackets are pretty cheap so unless you have a lot more time than money, I recommend not re-installing a used one. The other side to is that one has to waste enough time messing around with keeping pressfit BBs quiet; once you're going to the extent of removing the pressed cups, you really want to do everything you can to eliminate the creak once you have it all back together, and that means starting fresh.
What I recommend you do is pull the cranks, clean and grease everything (especially the spindle interface), and then reinstall them and check. Then make replacing the BB be the next step.