Gracias amigo pero no pasa nada:
C:\adb> fastboot flash recovery_ramdisk twrp_android_o_mate9_a1.img
target reported max download size of 471859200 bytes
sending 'recovery_ramdisk' (26982 KB)...
OKAY [ 0.585s]
writing 'recovery_ramdisk'...
FAILED (remote: Command not allowed)
finished. total time: 0.597s