"Again if further mutation is an addition or a change that makes it deadlier, who would you handle that."
I already answered that. You would handle is exactly the same way as if the current version of the virus mutates into something deadlier. Which, is, there is nothing you can do, but start from scratch. At that point you have a new disease. Should we start to worry if any of the influenza or other common cold viruses mutate into something deadlier?
"You seem focused only one scenario that doesn't represent what mutations are."
Sure, because this is the focus of the idea. You, not nature, select the mutation you want. You pick the one which is harder to mutate back. You seem to not get this point. I find it fairly intuitive.
"How? You are testing people with a live virus as opposed to a dead or weakened virus."
That is the other half of the point of the idea. The testing is already being done. There are people with mutations of this virus right now, probably more than 100 versions. This way we can trace geological history of the spreading. Of those 100, you select one that is not deadly (if that one exists), and spread it.
Lets say you manage to find 1000 people with one particular SARS-2 virus strain and nobody of those 1000 dies. You can deduce that that particular version of corona virus is much better than the current one, and you artificially spread this one instead. This has already been done for other diseases.
Notice that you actually do not give this virus to anybody, they already have it. Thus this method of finding it is safe. You do nothing. You just sample.
With a new vaccine candidate, you have to artificially give it to people and see what happens. Then you can't start with 1000, you start with 10, then 100, then more, and each step takes months.
"Far more people will obviously get sick."
This is why I think you didn't understand the idea.
"There is far greater chance of mutation to deadlier version."
Why? This is a virus that is already out there, you just try to find the one that gives mild symptoms. Why would you think this one has greater chance of mutation to a deadlier version?