(Hopefully) The final update on this:

Tickets issued with the original itinerary, with Taxes etc working to HKD 837 pp.

(Taxes lesser than originally quoted..and comparing with the same itin on LAN's website, seems to be the "DOMESTIC TRANSPORT TAX (MIA-7,5%) (US)" and some other minor item not being charged. I am not complaining! especially as LAN is charging USD 700 as fuel fine for the same itinerary!)

Over the past week, had a very helpful MPC agent (Thanks, Mr. L!) clearly spending a fair bit of discussing with LAN/looking up options.

MPC first issued 'interim' tickets to ensure that the confirmed segments were not cancelled by LAN. Then, they took, economy seats on a similaly scheduled flight - when
LAN removed the original GRU-LIM flight from schedules and told the MPC that the original flight was no longer operating, and since tickets had not been issued before it was cancelled, there was nothing they could do. The flight re-appeared a couple of days back, and (I guess) MPC kept arguing with LAN, while looking up alternative routing options for me. Seats released today finally and tickets issued immediately.

While I do foresee issues down the line (flights are well into the future, and I think LAN is quite notorious for playing with its schedules), I sleep a lot more comfortable now, having ticket numbers in hand - ones that are correctly reflected on LAN's site as well.

Oh and while I have no clue what the likes of SQ would have done for their elites in a similar situation, I am *very* happy with the MPC having spent time and effort liasing with LAN for me stuff like this makes me value MPC a lot!