Can You Use the Same Incision to Increase Breast Size?

If it is just a simple exchange to increase the size of your implants, yes, the transaxillary incision is fine. If you need a complex capsulectomy performed at the same time, your surgeon might suggest a different incision. Depending on how much "work" needs to be done to the pocket around the implant, more direct incisional approaches might give your surgeon better access / exposure, and you might end up with a better result.
You should visit with a board certified plastic surgeon and discuss your goals, listen to their suggestion and reasons for their preference. Good luck!

It all really depends on your specific situation and the skill of your surgeon. However, in most cases, the surgery can be done through the same incision without a problem. Good luck.

It is still possible to use the axillary approach. This will be a more likely situation if you have saline implants and are planning on staying with saline implants. I prefer to use an endoscope for my transaxillary breast augmentations.
However, I do not prefer to place silicone implants via the axillary approach. Most often, I will use the periareolar or inframammary approach for primary and secondary cases. Having said this, you should not fear the periareolar approach to your surgery as the scars, many times, heal beautifully.