Same operators, just the holding company of Merlin will be different. I assume that the same management and day to day operations will be the same. From the press release they are keeping it as a seperate company, same HQ and not distributing or changing assets of merlin.
Fingers crossed this helps with investment in the parks, if the parent company wants to invest more then there arent shareholders to block it based on profit. There is a full document on Merlins website about the plans. https://www.merlinentertainments.biz/recommended-offer/
The document also says that the two companies (Blackrock and Kirkbi) were there before public listing:
"KIRKBI and Blackstone jointly controlled Merlin in the 8 years prior to the 2013 public listing, during which time Merlin became the second largest location based entertainment business globally, and the partner of choice for the world's leading brands to deliver immersive experiences to guests."
So fingers crossed we go back to the investment days!