i think i'm facing the opposite, i want to lose all settings.. flashing sysupgrade image does not delete all settings ( -n from terminal or not retaining setting from luci), have to perform a factory reset after flash.. who knows 
i think i'm facing the opposite, i want to lose all settings.. flashing sysupgrade image does not delete all settings ( -n from terminal or not retaining setting from luci), have to perform a factory reset after flash.. who knows