Yet climbing Ayers Rock, as most other Australians knew the vast red monolith until recently, has long been a favoured pastime of tourists.
- source -
Is it better to use "which "instead of "as "in "as other australians knew..."
From K-12 Reader: emphasis added
A nonrestrictive clause (also known as a nonessential clause) is a type of adjective clause that provides additional information about a word whose meaning is already clear. A nonrestrictive clause often begins with the word which and are always set off with commas.
...Notice it says that "which" often begins the clause, but it doesn't always have to...
For clarity, this is the clause from your question:
, as most other Australians knew the vast red monolith until recently,
So, you are adding additional information that informs the reader, but is not required to distinguish one thing from another.
That leads us to connotation:
the associated or secondary meaning of a word or expression in addition to its explicit or primary meaning
Both "which" and "as" are acceptable. I personally prefer "as" because of the connotative feeling I get with it.
By using "which", it would feel like you are going to a kind of boring lecture mode, perhaps. But, "as" is more soft and conversational, open to other ideas, and isn't as heavy-handed. By using "as", this is still a nonrestrictive clause, but it doesn't feel as boring as one...
...as some may agree. (See what I did there?)