I have RMA scenario where the backup member is two-member VC stack needs to be replaced. Is the feature still applicable and are the any need-to-knows and/or best practices to look out for in order for the replacement to go smoothly?.
I understand the s/n must be updated on master to reflect new member.
About best practices, we don't have specific documentation, just the page you found. If you have the chance to upgrade the device first and then form the VC, it should be good.
If you still want to use this feature, because is easier for your environment, I think is OK, is safe. Since this a two member virtual-chassis, make sure "no-split-detection" is configured and yes, update the serial number if the configuration is preprovisioned.