On a HW routerboard, you can set the onboard serial baud rate (usually for `serial0`) with `system routerboard settings set baud-rate=<rate>`. Another way seems to be to press `s` during the boot process and select it that way. CHR shows only `routerboard=no` (for good reason; it isn't one), but this precludes you from using either `boot-delay` or the direct `baud-rate` settings.

The only remaining option appears to be to set the rate from `/port`. Attempts to change the rate from the line itself yield:

[admin@gns3-test] > port set [ find where name=serial0 ] baud-rate=1000000

failure: Cannot change port while in use!

I've also tried to coerce it to happen via `/system scheduler` firing an on-boot script to set the rate using `/port`, but on-boot still isn't early enough to catch it before the line is in use.

Is there a way to force RouterOS to relinquish the serial line (perhaps from a telnet/SSH session) or otherwise get around the catch-22? Any advice appreciated.