The SummitStack feature does not require a bootrom upgrade. You should not upgrade the bootrom of any node unless there are specific reasons to do so. However, the SummitStack feature does allow centralized bootrom upgrade.
You can download and install the bootrom to a specific slot using the slot parameter. The slot parameter is available only on stackable switches in the active stack topology. For information on upgrading the bootrom, see Software Upgrade and Boot Options.
If you do not provide a slot number, the stack attempts to download the bootrom image and install it on all stackable switches in the active topology.