@MaulaShaikh59472
It will never be 100% guarantee that any procedure is downtime free.
If you are dealing with network device in production, always consider the possibility of downtime
But, If you check the currenty priority of switches in the Stack and set the priority in the New switch prior to add It to Stack, there is a Very good chance the proccess run smoothly
Of course, switch must be on the same version and platform of current Stack.
