If you want to use external temperature measurement (not the ext. thermister or internal die temp) and write to the temperature register from your host then the most important bit is setting Tex = 1 in the Config register 0x1D. When Tex=1 the device ignores the other bits for thermister and die temp measurement but you can set Ten=0 for redundancy. You will then write directly to the Temperature register 0x08 and the average and max/min temperature registers will be updated according to the contents in 0x08. The m5 algorithm will then use these values for its calculations.