Can lipo change the shape of my butt from rectangular to more heart-shaped?

Without pictures we cannot make an assessment. Generally speaking patients who get the best liposuction results can be described by the triad of being “young tight and pudgy”.
Older individuals with skin laxity from lots of Scana last city and weight loss tend to be on the other side of the spectrum. Skin laxity can be deceptive and look like subcutaneous fat but 64 year olds can also have undesirable fat distributions that could potentially be improved with Liposuction. It’s unlikely Liposuction can contour your buttocks but again without pictures we can’t make an assessment.
Generally speaking people who are 64 years old are typically going to present with skin laxity due to loss of skin elasticity and weight fluctuations and this is not treated by Liposuction.
The type of equipment used is somewhat irrelevant in comparison to the skill and experience of the provider.
There is no particular secondary treatment or type of Liposuction that gives any significant skin tightening that’s better than traditional Liposuction. Consider re-posting it with proper pictures. Pictures should be taken the way plastic surgeons take before and after pictures. Generally pictures should be taken using the timer on your camera or have someone else take the picture from about 8 feet away showing your torso from your neck to your knees wearing undergarments showing your front, side and back side standing in a neutral position.
Delivering consistent quality liposuction results is more difficult than most people believe it. This includes plastic surgeons. Simply being a board-certified plastic surgeon was good reputation is insufficient to assure that the provider has mastered body contouring with Liposuction.
Liposuction results are permanent and irreversible and if done poorly can leave people disfigured.
I cannot emphasize enough the importance of choosing only the most talented and experienced providers for this procedure.
Do that by having multiple in person consultations with local board-certified plastic surgeons in your community. During each consultation ask each provider to show their entire collection of before and after pictures. Being shown a handful of pre-selected pictures which most likely represent the best results of the providers career is insufficient to get a clear understanding of what average results look like in the hands of each provider. An experienced provider should have no difficulty showing you at least 50 sets of before and after pictures. Highly experienced surgeons will have 100’s or even thousands of before and after pictures for common procedures like abdominal liposuction.
Ask the provider to show you previous examples of other patients with similar body characteristics and in your case similar age. ask the provider to show examples of excellent outcomes, average outcomes and less than outcomes.
Continue having consultations until you feel like you found a surgeon who can meet your needs.
Keep your expectations on the low side. From what you described I am not convinced Liposuction is a great procedure for you.
Best,
Mats Hagstrom MD