Something you might not have noticed, is the fact that you can not change or modify the guestOS type after a virtual machine has been created in the new vSphere Web Client, this option is just grayed out.
Note: A feature request/bug has already been filed with VMware to have the ability to change the Guest OS and Guest OS Version for a virtual machine after creation in the vSphere Web Client.
Here is an example of a custom workflow that I created called Change Guest OS Type and as you can see that it only shows up under the context of a virtual machine object in the vSphere Web Client.
From my perspective, the use cases are endless as you can create ANY custom workflow to perform any action or series of operations that can span across VMware products as well as 3rd party systems and directly present them to your end users in the new vSphere Web Client. Not only that, users can specify which workflows they see by default on a given vSphere object and this can differ from user to user based on their daily set of tasks.
So going back to our scenario, here is a way to change the Guest OS and Guest OS Version using a custom vCO workflow.
Step 1 - Download Change Guest OS Type vCO workflow to local desktop.
Step 2 - Open up the vCO Workflow Client, you can do this by pointing your browser to your vCO Server and click on "Start Orchestrator Client" link.
Step 3 - Import the Change Guest OS Type vCO workflow from your desktop to your vCO Server
Step 4 - Next, we need to go to the vSphere Web Client to make this vCO workflow available on a particular vSphere object, in our case it is a virtual machine. On the home page of the vSphere Web Client, click on "vCenter Orchestrator" icon in the center pane or select it from the navigation pane on the left. Once you are in the vCenter Orchestrator configuration page, select the "Manage" tab and click on the "plus" icon.
Step 5 - Locate the Change Guest OS Type vCO workflow on the left hand side and then click on the Add button. Finally, select type to be virtual machine as this workflow is only applicable to a VM and OK to save the settings.
Finally, it is time to test drive our new workflow! Locate a virtual machine and right click on the object, in a second you should see a sub-menu for All vCenter Orchestrator Actions and then select our vCO workflow Change Guest OS Type which will start off a very familiar wizard.
The first screen is the object selected, which in our case is our virtual machine. You can of course change this, but we will leave it as it's context was automatically picked up.
Though the functionality of changing the Guest OS is not available in the new vSphere Web Client, you can still provide the same functionality to your end users through a custom vCO workflow which are now tightly integrated into the vSphere Web Client. Hopefully this sparks some ideas on other vCO workflows you can create or expose through the vSphere Web Client in your own environment. I know I have a few in mind :)
A big thanks goes out to Christophe Decanini for helping me with a few questions while creating this workflow.