User name not changing on Windows 10

One of my colleagues, In the new environment, he settling into all users are utilizing local profiles in Windows 10. There is no domain established at this time but it is a project he is working towards and it will take some time.

The user names established for the local profiles do not have a common naming convention. To make the PCs more logical to work with he is looking to implement a common naming convention across all PC profiles for the users.
It is very easy to change the account name/display name within Windows 10. However, it does not change the user name associated with the profile.

Under admin privileges, he ran netplwiz to bring me to the User Accounts menu. he selected the user name he needs to change and went into properties. Under properties, it has three fields: User Name, Real Name, and Description.

He attempted to change the user name field and apply it to the PC. When he tried to apply the change he receives the below message:

“The user name for PCName\UserName could not be changed.”

He did not conduct the initial deployment of the desktop PCs so he was unsure as to what would prohibit changing the user name.

He ran a test on his PC, and he had no trouble changing the user name.
Any suggestion.?