hi are you just adding another switch to the ring ? if its already formed an you dont break the ring you can add remove cables without dropping whole stack but there is things to watch out for
they can be plugged in while powered up
https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst9200/hardware/install/b-c9200-hig/b-c9200l-hig_chapter_010.html Power off a switch before you add it to or remove it from an existing switch stack. If changes are made to the stack without powering down the switches, the following results can occur:
If two operating partial ring stacks are connected together using a stack cable, a stack merge can take place. This situation reloads the whole stack (all switches in the stack).
If some switches in the stack are completely separated from the stack, a stack split can occur.
A stack split can occur on a full ring stack if:
More than one running switch is removed without powering down.
More than one stack cable is removed without powering down.
A stack split can occur in a partial ring stack if:
A switch is removed without powering down.
A stack cable is removed without powering down.
In a split stack, depending on where the active and standby switches are located, either two stacks might be formed (with the standby taking over as the new active switch in the newly formed stack) or all the members in the newly formed stack might reload.
