Removal of cabin on GUF'd flight
 

Recently booked flights that include SMF - PHX - PHL - LHR in which the PHL - LHR leg was GUF'd from J to F. 'Twas meant to be the 787-10 (in March). It's changed to an A35K (which I wouldn't be upset about if I was in J).

Before I ring to change to a flight with F, am I right in understanding I should be able to change the connection point? Would I be able to change both connections points? I.e. fly SMF - LAX - JFK - LHR?

You will be allowed to re-route. You might have some push-back on a LAX-JFK if you are trying to get into F on the TransCon. But if you went SMF-PHX-JFK-LHR, I cannot see a problem.

I would specifically contact YouFirst on this, once you have checked available seats on alternative services. It's a lot easier all round if there is A bucket availability, so I would check those options first and then call up. I think LAX - JFK would be OK, but only in the same cabin as PHX-PHL. Check also routings via BOS and ORD.

Have had a similar issue (albeit on an Avios upgraded ticket, not GUF'd) and ended up on the transcon in J.
Compared to your original routing that's still a (massive) upgrade and should not lead to any pushback from YouFirst.

To be honest I'm not so worried about the transcon. I'm not expecting F and I know the A award availability is lacking. Either way I'm actually relatively happy with "domestic first" for a sector like PHX - PHL. Ideally I'd like a better airport to connect through on the West Coast but I think Phoenix is the best it's going to be. LAX would be via the Eagle's Nest for the flight from SMF.