Depending on context, yet and as yet can mean different things.
Merriam-Webster has a specific sense of as yet that it defines:
3 : NEVERTHELESS, HOWEVER
as yet
: up to the present or a specified time
// there are as yet few clues
— Sharon Kingman
This is in contrast to the primary sense of yet:
1 a : in addition : BESIDES
// gives yet another reason
In your specific example, both as yet and yet are very likely to mean the same thing, which is:
But if there be any still unfit to be called a son of God . . .
However, as yet could have a subtly different implication of something that is more likely to change in the short-term, or something that is, surprisingly, still as it is.
There is no cure for cancer yet.
There is as yet no cure for cancer.
There is a difference in terms of the specific grammar used in this particular case, but there is also a very subtly different sense of of expectation in the second version, and a very subtle implication that a cure is less far off.
Having said that, for all intents and purposes they mean the same thing.
Best Answer
These are nearly synonymous phrases. Within is being used as a preposition to indicate that you are referencing the area inside of the radius in relation to the radius. In basically communicates the same message, but with less focus on the actual radius.
However, “within” and “in” are not always interchangeable. “Within” describes an object’s placement for location and time.
“Within” is specifically used to describe the boundaries of a location or time, consequently placing a larger emphasis on constraints. “Within six hours” implies that something will happen before six hours. However, “in six hours” suggests a more flexible time range (something will happen in about six hours).
“In” is used for a wider variety of situations, such as inclusion (there are many more), and is used in many idiomatic expressions as well.
Additionally, the word “meter” in your phrases should be plural because multiple meters are modifying the radius.
To answer the second part of your question, I believe “on the border/edge/circumference of the circle” most clearly communicates that you are referencing the border of the circle and not the area it encloses.
Another note: you can rewrite the phrases as “within/in a 10 meter radius” to make them more concise. This has no effect on the meaning.