Well, all very interesting, and stressful for me.
I cannot change my schedule. LATAM will not let me. They will not let our travel agents change the booking. The local LATAm agent here in Belo Horizonte will not change to an earlier flight either.
So how about cancelling the 5pm flight and I'll separately rebook on an earlier one? No. LATAM will then cancel all my schedule, as the flights are 'linked' and because I didn't show up on one of the six flights, everything is then cancelled. So I'd then have no London flight to get back home.
All they can do (apparently) is to say get to Brasilia airport early on Friday, and if there is room on the two earlier LATAM flights to Sao Paulo,I can change my ticket there and then. There are seats available at the moment on both flights. But apparently this cannot be done in advance.
This is what both my travel agent and the LATAM agent has told me. Chuffing ridiculous. So I have to stress until Friday, and then still may have to run the gauntlet of Friday evening rush hour, Sao Paolo style.
This may be the stress talking, but I think it's disgraceful from LATAM. I've travelled a fair bit, with a planned schedule of flights sometimes, and never come across this bizarre farcical policy of theirs.