Your question is really beyond the expertise of most laypeople. I ran some references in my copy of "Fasting and Eating For Health", but could not find any definitive answers there. Fuhrman does talk about how the typical high animal product diet is affecting the hormone levels of modern people (pp 35-36,. He also addresses how fasting or underfeeding can affect the immune system (page 69).
I have a feeling you may need more than just a forty day fast to accomplish your goals. While its true that excess estrogen is stored in body fat, fasting alone may not result in a cure. I would imagine that most excess fat would need to be eliminated before the body would start catabolizing tumors, still, I have read anecdotal accounts of that happening. How much experience do you have with fasting? How much extra fat do you have? What has your diet and lifestyle been like the past decade or so, in other words, how toxic are you? Will your health practitioner be there to guide and supervise you through your fast? All these things will be factors in the ease and safety of your fast.
To answer your questions, a teaspoon of lemon juice will not stop the body from breaking down fat. I mean people can lose weight eating almost anything as long as they eat fewer calories than the body demands. What does happen when any kind of carbohydrate is consumed is that the carbs are broken down into glucose and the body does not enter into full ketosis, that is where the body digests its adipose tissue to produce ketones to fuel the body in the absence of glucose. The use of herbs and other supplements are generally discouraged when water fasting. The body may react to them in a negative way. Psyllium and Bentonite should never be used during a water fast, the digestive system needs to shut down and allow the body to use that energy for cleansing and healing. Enemas may be used to clear the toxic bowel, but even this practice is frowned upon by some experts.
The liver is said to be responsible for hormone levels in the body. I don't have my reference book nearby, but a congested liver can cause estrogen to build up and be stored in fat cells. My naturopath predicted that many of my "female problems", PMS, cramping, clotting, heavy flow, and even monthly migraine headaches would be improved once I got my liver functioning better through proper diet, herbs and flushing. He was right, it took about six months of every two week flushes, but my periods are trouble free for the first time in my life. If the liver is functioning properly, you will not have to worry about fat released estrogen being reabsorbed, it will be broken down. You might want to try a few flushes before beginning your fast. I can't guarantee results, but it sure helped me. Also, you may want to do your psyllium based bowel cleansing before you fast if you feel this is needed. Drinking ample water is all some people need to improve bowel function. Most important of all, try taking a few weeks of eating a very healthy diet. Fuhrman recommends all vegetarian, no fats or animal products for six weeks. This is an excellent pre-fast cleanse, you can do your liver and Bowel Cleanses during this time if you want to try those. Also you can try fasting one-three days at a time to further cleanse your system and prepare for your longer fast. All of this may be unnecessary if you will be doing a closely supervised fast; but if you are going to go it alone, you need to be well prepared. Good luck, please keep us posted on your decisions and progress.