If coronavirus mutates, will it make it more dangerous or less dangerous?

It could go either way.

It's already mutated.  11 strains, so far.

Hard to say. But it would definitely derail their work on finding a vaccine. 

probably more dangerous because it would make finding a vaccine more difficult i presume.

Racoon City is already a mess.

more.

the original will still be here, and the new one will be immune to any vaccines that may have been developed. 

You don't know which one.  it's like flipping a coin, heads it gets worse, tails it gets better.  Most mutations however are not beneficial for the organism, only a very few are.

This is not a question about Chemistry.  It needs moving to Biology or Medicine.