Chin implant and age - do you have to take them out and modify them only once, or does this need to be done every few years?

Chin implants tend to remain without problems for years or decades. Chin Implants are made out of solid silicone so they should never have to be replaced and they are soft enough to where they won't erode the bone. They are replaced only if there are complications or because the desire result was not accomplished.

Is it possible that you are thinking of the typical and very problematic off-the-shelf implants, which are often replaced, removed, and more due to an array of problems?
If they are off-the-shelf implants, likely they will have to be addressed at some point for an array of reasons.
Custom chin implants are not perfect either, but they are made exclusively for you and provide the best solution as far as implants are concerned. Before making such an important decision, please learn the differences between standard and custom chin implants.
Good luck!