I used method two and set GCF today and that got SA and all bands enabled on both SIMs. I don't care about NRDC since we don't have mmWave here but I got a new T-Mobile MVNO SIM the other day and was shocked to find it has SA disabled by default.
Unfortunately I just forced SA and it was kicked from the network. Seems that T-Mobile is still not giving SA access to all MVNOs automatically, even ones with the 240 SIM cards.
That's something I didn't even think about. If I don't have to re-enable RAT selection every time I reboot when using an AT&T network SIM, that would be awesome.