Impressive that corals have such a survival mechanism. But hopeless if no other species of algae can enter another symbiotic relationship with them?
TLDR Yes but it's complicated. There are more suitable algae species but AFAIK coral under heat stress will still often expel the algae even if the algae isn't the one stressing the coral. So you have to essentially breed a more tolerant coral and then provide the algae.
Now luckily there do exist more heat tolerant coral and algae species living alongside each other. Unfortunately those species are located in the Persian Gulf/inside the Strait of Hormuz so they are regularly subject to added stressors from Oil/NG extraction, military conflicts, and waste dumping. And of course their location makes research on them/collaboration between research institutions complicated.
And it's not like you can just transplant these coral somewhere else and they'll live. They are adapted to their environment and that environment plays a part in their heat tolerance as well. But research on these coral ecosystems will likely shed a light on how to help other coral species to adapt and evolve.
Maybe the pharmaceutical industry can target a new market here...