If you have the BGW210 gateway there is a written series of steps for root here: https://github.com/Archerious/bgw210-root As well as step by step configuration for complete gateway bypass on Mikrotik router hardware here: https://forum.mikrotik.com/viewtopic.php?t=154954

If you are stuck with the newer XG-PON hardware, it looks like you might be out of luck for now.