No, the OW tool never offers codeshares, I had to get QF to do that myself.

My understanding is that alone isn't a ticketed points change and would fall under the same exemption as a date / time change. But I have always done them during other changes so not 100% sure on that. The last time I did it was on my CX ticket, but I was able to do it before ticketing since CX doesn't accept payment in the OW tool, you still have to call in for a payment link. Prior to that was another QF ticket and I had an invol reschedule so got free changes together with that.

This is one of the most frustrating things about RTWs and crediting to programs that calculate by revenue... you have to scratch and dig to put everything possible on codeshares that credit by distance. I've had AAdvantage go both ways on AA coded flights so just won't risk it on long segments. JL used to have a few codeshares to South America in the past, I know I've flown to GIG on one right before COVID started but looks like GRU is the only one remaining. I definitely wouldn't have gone to Brazil if I knew I could get distance credit on AA codes, would much much rather have gone to Argentina... but c'est la vie (I'm quite put off by Brazil's return to visas for US, Canada and Australia citizens, but my old 10 year visa is still valid until October). Haven't been to Florianopolis yet so that's an option at least.