my two cents are: that is not recommended, the reason the upgrade is part of an automated process (ESXi hosts, nsxmgrmg, edges, etc.), and sequence should be care, also is recommended to have mode than one EDGE VM.
check this for more info in formal way: https://docs.vmware.com/en/VMware-NSX-T-Data-Center/3.0/nsxt_30_upgrade.pdf