Here is an example of the error trying to use vCLI to put an ESXi host into maintenance mode:
Here is an example of the error trying to use PowerCLI to power on a virtual machine:
I personally think the error message should be updated to be a bit more clear and state that this particular license type (free ESXi) does not allow for any changes using the APIs. There is a small VMware KB article regarding the configuration of Jumbo Frames using the vCLI, but as you can see this error is not just applicable to vCLI but across the vSphere API/toolkits.
Now there are three types of licenses I consider an ESXi host can be configured and we'll walk through each of them. In the following example, I will be using the vSphere SDK for Perl script licenseManagement.pl to demonstrate the various license types which is allowed since it is only querying the license information which is a read operation to the APIs.
1. Evaluation License - When you first install vSphere Hypervisor (free ESXi) and before applying your free license key, the host is automatically configured to be in this mode. In the evaluation state (60 days), you are basically licensed with ALL features just as if you have paid for the highest license type which is Enterprise Plus. You have full read and write access to the vSphere API and all the various vSphere toolkits for 60 days as part of the eval, once the 60 days are up, you will be configured just like the free version of ESXi.
Here is an example of querying the license information for an evaluation ESXi host:
Here is an example of querying the license information on a free ESXi host:
editionKey which is the first column and the name of the license in the second column which is "vSphere 4 Hypervisor" which represents the use of the free edition/license of ESXi. Both of these string text can also be used in conjunction to determine programmatically that you are running the free edition of ESXi.
If we take a look at the vSphere Client we also notice the list of features is quite small compared to the evaluation version:
vSphere Edition Comparison chart.
There is not a specific license feature that allows for the read and write access to the vSphere API and toolkits but by using any of the paid editions, you automatically have complete full read and write access to the vSphere APIs and the various vSphere toolkits.
Here is an example of querying the licensing information on a host with Enterprise Plus license type: