Migrating to Office 365, need help with a potential roll-back solution

We currently have an one on premises Exchange 2013 server and are moving to Office 365.  We are not going to maintain a hybrid scenario and are performing a cut-over type of migration. So once we complete the DNS changes and final passes of the migration we will decommission the on-prem Exchange server.

I was instructed to make the following changes to our Active Directory SCP so internal Outlook clients will look at the Office 365 servers when autodiscovering instead of trying to find our internal server:

 Command 2: Set-ClientAccessServer -Identity "CAS1****" -AutoDiscoverServiceInternalUri $NULL

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(Where CAS1 is my Client Access Server)
Also the internal DNS changes will be performed for the autodiscover CNAME.

That seems pretty straight forward, but as a conservative planner who has been burned enough times I want a solid bailout plan.

I want to allow a way to roll back if there is a problem after I run the above command.
In other words, I want to know how to undo that command.

Thank you in advance!
I was provided by support with this command as an answer to that question:

First run this before changing the CAS:

Get-ClientAccessServer | Select-Object AutoDiscoverServiceInternalUri

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Take note of the result and then run this command:

Set-ClientAccessServer -Identity “CAS1” -AutoDiscoverServiceInternalUri "https://cas1.cumulus-apps.com/Autodiscover/Autodiscover.xml"

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Replacing https://cas1.cumulus-apps.com/Autodiscover/Autodiscover.xml with the output I made note of from Step 1, as well as replacing CAS1 with my actual server's name.

The problem I am having is that when I run:

Get-ClientAccessServer | Select-Object AutoDiscoverServiceInternalUri

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I get a blank result as seen in the first command in the screenshot below.

Can you you please provide me a way to "roll back" if something goes bad.
I want to cover all my bases before we go-live if possible.

More details:


Thanks in advance!