for access to k510 people use z550_p3k_dcu.49R.ssw (this is that special main). flash takes around 15 sec.

leater in far use w300_w810_z550_cid49 script to enter


but if i remember correct, far can`t let you access to FLASH folder in k510
it`s not supported

i mean you cant flash your FS and MAIN using only far because you have only access to FS part, not MAIN memory of mobile.