Almost all surgery can be repeated. Still for most patients this is not needed. As time passes you may find that you need to modify or "update" something that was done several years ago. This is usually not a problem.
After breast augmentation there are two main reasons why surgery may be needed. The first is that as time passes the effect of gravity may change the breast shape. In these circumstances tightening of the breast may be necessary. This is called a mastopexy, and it is not usually necessary to remove the implant during this operation.
The second reason is if there are concerns about the integrity of the implant. With saline implants loss of integrity usually means that the implant leaks and deflates. This is usually obvious. With silicone gel implants loss of integrity is not obvious, and may be impossible to detect. Older implants sometimes ruptured and would cause a change in shape. There is no good scientific evidence that this caused significant medical problems. With the new implants the material is more cohesive and resembles a solid. How long this lasts is not known. However, changes made by the manufacturers have made the implants very strong. The FDA suggests that MRI scans may be used a few years after surgery to check for the integrity of the implant. Unfortunately MRI scans to have a significant incidence of false positive results. This means they may suggest problems with the implant when in fact the implant is intact. This may result in unnecessary surgery.
In all implants, in the breast or elsewhere in the body, shedding of molecular silicone from the implant into the layer of scar tissue around the implant often occurs. There is no good scientific evidence that this is a significant concern. All of these are topics which are constantly reviewed by plastic surgeons, the federal government, and the manufacturers of implants.