Are there alternatives to general anesthesia that can be used when getting butt implants?

With a history of blood clots and pulmonary embolism, I understand your concern. That being said, there are a couple of important things to consider. Number one and maybe most importantly, is to go to an experienced reputable, board-certified, plastic surgeon, who specializes in buttock implants. There are an extremely few number of these throughout the country, even the world, so make sure to do your research before selecting one.
Specifically regarding the blood clot issue, much more information is needed before any safety/preventative recommendations can be made. Is it that you have some sort of clotting mechanism abnormality that put you at high risk for blood clots, or was it the type of surgical procedure performed that is high risk for blood clots, and/or were the typical necessary precautions simply not taken in your last surgery to prevent blood clots. All of these things need to be addressed. If it is that you have a clotting mechanism abnormality, there are additional measures and medications that can be given immediately before surgery and continued for several days thereafter to greatly minimize your risk of blood clots. Hope this helps.