After unlocking, you need a custom recovery like TWRP to flash the new ROM.
A: Hardware-wise, yes. Both share the same 6.01-inch AMOLED display, Snapdragon 660 processor, 4GB RAM, and 64GB storage. The key difference is that the R11st is the China Mobile carrier edition, while the R11s is the standard retail version available in other channels. oppo r11st global rom exclusive