Well, you cannot disable it, but you could try setting the update routerboard to yes:
http://forum.mikrotik.com/t/cannot-change-boot-mode-to-swos/181666/1
https://help.mikrotik.com/docs/spaces/ROS/pages/30474317/CRS3xx+CRS5xx+CCR2116+CCR2216+switch+chip+features#CRS3xx%2CCRS5xx%2CCCR2116%2CCCR2216switchchipfeatures-DualBoot
Starting from RouterOS version 7.17 device-mode restricts SwOS/RouterOS transition for dual-boot; in order to enable: system/device-mode/update routerboard=yes