Maybe try this, as I'm not 100% sure.
On the Yongnuo, switching to wireless slave mode, keep your finger for 2 seconds on the ZOOM/”lightning bolt” button until the flash icons appears with blinking “OFF” label. Pressing the right key on the 4-way controller activates wireless slave mode – the display changes from “OFF” to “SL on” with an additional “slave” icon on the display.
Then go to the flash menu on the X100T and select Commander.
I think it should give you cordless off camera flash, using the flash in manual mode for correct exposures.
Will the built in flash as commander add to the exposure of the shot? Or just the external off camera flash will add to the scene?