This article describes the strange workaround of switching VMware NSX-T enabled cluster from using vSphere Enterprise Plus license to vSphere Standard license with vDS licensed through NSX-T. I really hope that you will not need to go through this as it is quite like bringing the whole environment up from scratch. But if you have two clusters with enough resources it will enable you to do it without downtime.
Environment on which this was tested is vSphere 7.0.2 and NSX-T 3.1.2
NSX-T as a network and security platform enables network functions to be virtualised on your vSphere cluster. The way it does this is to implement additional features of network traffic steering and packaging inside its vSphere Distributed Switch (vDS).
Before NSX-T 3.1.1 the only way to get your cluster equipped with vDS was to have a vSphere Enterprise Plus license. From NSX-T 3.1.1 version onwards, VMware gives you the possibility to use vDS without vSphere Enterprise Plus license and license it using NSX-T license. This enabled users with a standard vSphere license to be able to deploy NSX-T on all editions of vCenter Server and vSphere.
After this started to be possible there were some customers who realised that in some cases the only reason they have vSphere Enterprise Plus license for a specific cluster is to be able to use NSX-T since that was needed in the past. So they decided that they will transfer those Enterprise Plus licenses to some other (new) cluster that needs those licenses for more different features.