Anyone who applied before they stopped Test and Go can still come under the same conditions, no matter when they arrive. Only change is they have to take a 2nd PCR test after a few days at the government's expense.
I read somewhere that Guy Pearce stepped in at the last minute when the original actor dropped out as he's a friend of Winslet. So he's maybe not playing such a key role. Naturally he will now turn out to be a wrong 'un.