Can Coronaviridae mutate into something as dangerous as Flioviridae?
Each existing virus can mutate until it becomes ready to affect new species, organisms, cells or whatever.

Coronaviruses too are capable of mutating, so they could become more dangerous.

But can coronaviruses (which cause respiratory tract diseases) mutate into filoviruses (which cause hemorrhagic fevers)?

Of course not.

Filoviridae and coronaviridae are two different families of viruses, like felidae and canidae are two different families of mammals, in the order carnivora.

And you would never ask if cats can mutate in dogs!