Each CFA nominates a set list of referees at levels 7-5 to act as assistant referees only early round FA Cup games, FA Vase games and the FA Youth Cup. The FA then make the appointments for these games centrally, the referee will always be level 4 or higher and they will always have at least one level 5 to take over if the referee gets incapacitated. Once contrib teams get involved that's the end of the journey for those on the nominated list as they will then use their panel of level 3s and 4s, the only exception might be when a contrib team plays a supply league team and they might use a level 5 on one of the lines. Assistants for replays in the preliminary rounds of the FA Cup are made directly by CFAs, the FA only appoint the referee.
For the other FA competitions, so Women's FA Cup and FA Sunday Cup, the FA give a list of the early round fixtures to CFAs and ask them to appoint