Rcur-
Not sure anyone other than your surgeon can answer that and you should probably discuss that with them. I can tell you I had the same symptoms prior to my bilateral HR surgeries, tried for years to stretch out the shortened muscles and correct the pelvic tilt with exercises that only ever resulted in short term relief. It took a few months of recovery after surgery to get those muscles working properly through PT and regular daily stretching, walking and gym work but all of the symptoms resolved themselves positively including the pelvic tilt and being about to enjoy my 3rd year anniversary there is no indication of reverting to any kind of a problem. My sense of it is there would be no concern of cup shifting as the muscles re-lengthen but your surgeon should be able to explain the reasons or concerns to you more specifically. It's a life saving/changing surgery the vast majority of OA sufferers find give the relief from the chronic pain and restrictions and offers a tremendous improvement to the quality of life. Best of luck.