Would a weight loss of 5 to 10 kg improve the final result? If yes how long PO do I have to wait to start a food rebalancing?

About 50% of the fat that is transferred lives and becomes a part of you.  This will hold stable as long as there is no weight fluctuation.  The fat will not move, but losses in weight will distribute differently. The fat that lives in the buttocks from the procedure will get larger with weight gain and smaller with weight loss. Most plastic surgeons will recommend that vigorous exercise be postponed until six weeks after surgery.
Kenneth Hughes, MD, ABPS Board Certified Plastic Surgeon
Los Angeles, CA

Hello dear!
Thanks for the question and provided information as well.
After a BBL, you lose or gain weight in the same way as before. So, if you lose a considerable amount of weight, the results of your surgery will be affected.You are still early on the healing process, it can take up to six months to see your final results, so please be patient. At the stage you are in, inflammation is normal.
If you have any concerns, I suggest you to follow up close with your plastic surgeon.
Good luck :)

I think it's a little early to be talking about changing your outcome through weight loss. At this time you're still early in the healing process and you should be focusing on maintaining adequate nutrition. Each provider has their own protocol in regards to exercise after surgery and you should follow what your doctor recommends.  I encourage my patients to start exercise three weeks after the procedure but tube stain from any excess movement or activities within the first three weeks.  Generally speaking you will always maintain a new fat distribution after liposuction with that transfer. Most patients don't look good being overweight. It's true that weight loss will shrink the size of your buttocks but also the rest of your body. The best way I can describe this as you will have a permanent new fat distribution and you can be a large overweight version of that or a small petite one depending if you're overweight or at a healthy weight  In the end weight change should be based on a permanent lifestyle changes. You have a lifetime to figure out what's the ideal weight for you and where you're comfortable and what you're able to achieve it.  Best, Mats Hagstrom MD 

Hi and welcome to our forum!
At three weeks post surgery, you are still experiencing significant inflammatory swelling (as expected) which obscures and distorts the operative result. 60-80% will subside by the 6th week, with the remainder slowly subsiding over 6-12 months. There is no way to differentiate between swelling and residual fat this early on. 
A 10 kg (22 lb) weight loss will most likely result in diminution of your BBL result as you will resorb body fat from all areas.
As every plastic surgeon has their own individual protocol for diet and activity resumption after surgery based upon lifetime surgical experience, I recommend you discuss this issue with him / her. 
Best wishes...