Is it possible and safe to have a second breast augmentation?

Yes. A second augmentation implies the first implants were removed and not replaced. Performing an augmentation again is possible and safe if the surgeon is experienced in such procedures. There are alot of nuances in obtaining a good reult.
Yes. It is certainly safe to have an implant exchange- and the recovery is often easier than the first time around.
Depends. If what you mean is if you can have your implants exchanged for larger one, then it is a very safe and usual procedure.
Yes. It is absolutely possible and safe to have a second breast augmentation. In fact, breast augmentation patients typically need some sort of revision every 10-15 years on average (but not always). This can include release or removing the capsule that forms around the implant, changing the size, location, or material of the implant, or combining other procedures such as a breast lift.