Is it possible to run a script once after reboot ??
Once as in really only once and then never again, not even subsequent reboots ?
Don’t think so without other scripting to change things.
But it is possible to have a script run after each reboot.
Use scheduler and set start-time=startup
See also https://help.mikrotik.com/docs/display/ROS/Scheduler
Yes,
1st case, only one time after reboot, everytime the machine reboot:
/system scheduler
add name=everytimeonreboot  start-time=startup interval=0s \
    on-event=":delay 20s;\r\n/system script run <SCRIPTNAME>"
2nd case, only one time after reboot, but just for next reboot only:
/system scheduler
add name=onlyonetimeonreboot  start-time=startup interval=0s \
    on-event=":delay 20s;\r\n/system script run <SCRIPTNAME>\r\n/system scheduler disable onlyonetimeonreboot"
for execute again on boot, simply enable again the scheduler
As I said,  additional scripting to disable things.
Nicely done !
3rd case, only one time after reboot, but just for next reboot only, self-destruction scheduler:
/system scheduler
add name=selfdestructionscheduler start-time=startup interval=0s \
    on-event=":delay 20s;\r\n/system script run <SCRIPTNAME>\r\n/system scheduler remove [find where name=selfdestructionscheduler]"
for execute again on boot, you must add again the scheduler.
Thanks 