There are 3 things to know when it comes to the female breast and training.
Weight loss and loss of bodyfat:
Genetics may determine if your breasts will shrink drastically or if they will be uninfluenced when you LOSE FAT. There is not much to prevent this from happening. Some might find it a welcome change to have smaller breasts The only 'natural' way to influence their size is to keep your bodyfat percentage higher, as the female breasts are mostly made of fat tissue.
Training with bigger breasts:
Just as in your every day life, you might need to ensure you wear sports clothing and underwear that leaves little room for the breast to move freely, in order to prevent injuries. Also avoid exercises that would put pressure on your breasts, or any other form of heavy impact. The female breast tissue is very sensitive, prone to injuries and known to react easily with ulcers.
The advice for training with implants/augmentations is mainly the same as for training with bigger breasts. Avoid exercises that put too much strain on the chest area, and avoid impacts and collisions with training gear and weights. Contact your doctor in addition for more insight about what precautions you have to take when training with these.
NOTE: Don't use regular bras with metal or hardplastic supports in the gym or for sports, they can cause injuries and create pressure spots.