Could time be used to create coronavirus virulence in some other timeline, with results forced into our present?

That is always possible and has been done with respect to a number of disasters that have befallen humanity. This is done on a regular basis by the Extraterrestrial Alliance to change the past in a way that will benefit their progress in the future by going back in time and re‑engineering things and changing key events they believe will bring about future changes favorable to their aims. So this is done routinely and can be applied to optimizing bioweapons as well. They can try them out in the future and in some ways that is an advantage compared to trying them out in the past because that would destabilize the present moment they wish to work from and influence in the best way.