I don't completely understand what you mean by "without replacing it"
Changing the VM formfactor will always mean it needs to be re-deployed with the new size.
nsx-v: “Change appliance size” is only applicable to ESGs. This will perform a “redeploy” with a new appliance (vNIC MAC addresses will change).
Or are you just asking for (if any) api call associated with that resize process ?
nsx-v api call for resize and redeploy:
page 514 (size)
page 351 (redeploy)
Not that i am aware of. Maybe someone from vmware can give an answer on this.
Afaik you need to create a new edge with a bigger formfactor and then replace the old one with the new one.
Deploying edge via api: https://code.vmware.com/apis/976/nsx-t
"Create a Transport Node"
and to replace the edge via api
"Replace the transport node in the specified member of the edge-cluster"
The process for changing the edge node size:
1) Deploy a new edge with the desired size;
2) Go to System > Fabric > Nodes > Edge Clusters;
3) Actions > Replace Edge Cluster Member
With this a new edge with larger size will replace the smaller one.