Considering butt implant removal and replacement, 25 years post op - can this be done at the same time?

Good question, indeed your current implants can be removed and replaced with a better size and shape buttock implants. Because your current implants are breast implants, they are round and spherical, thus not anatomically shaped. A much more appropriate shaped implant for the buttock is the Stanton Anatomic™️ buttock implant which is a symmetric oval. This shape best conforms to the anatomic natural anatomic shape of the gluteus muscles.
Please keep in mind that an extremely few number of board-certified plastic surgeons specialize in buttock implants so be sure to consult with one that is reputable and experienced. Unfortunately you may have to travel long and far away from home to find this particular surgeon. Glad to help.

Dear Honest,
Posting your pictures - back and side views , would have been helpful . The answer to your question is yes. However, your current sub muscular implants will have to be removed and in my practice, your new implants will be placed sub fascial - on top of the muscle. I have done many of these surgeries. You will have to decide if you want round or oval implants and how large do you want your buttocks to be.
Always, consult with experienced board certified plastic surgeons who operate in accredited surgery center for your safety. Most importantly, check the before and after pictures in the photo gallery, to make sure that they are numerous, consistent and attractive with natural look.
Best of luck,
Dr Widder
widderplasticsurgery.com