Hmmm, in Control Panel > Administrative Tools > Computer Management, I have:
System Tools
Storage
Services and Applications
I started opening these folders and their sub-folders looking for "Local User and Groups". There are hundreds of folders and sub-folders, so after a while I gave up and resorted to a Registry scan, my usual solution to such puzzles. There I found "Local Users and Groups" to be a snap in to the Microsoft Management Console, a feature about which I had long ago forgotten. The Console I mean, otherwise known as MMC.
I found and checked my MMC and I don't have "Local Users and Groups" snapped in. I finally gave the project up, as I was getting sleepy and had already discovered the solution.
You change it in your Microsoft account on line. It's called "Display Name". I changed it there and it trickled down to my machine.
I can only wonder why two different installations of 8.1 have different control panels.
Perhaps Microsoft has implemented a "Which Coast" switch as a first phase of their upcoming GPS feature. This feature, due in Windows 10 (which will also be known as Windows Galaxy Control) , will enable them to relocate users to balance internet traffic. It seems there is far to much traffic going to Maryland and California. Moving users to New Mexico and North Dakota should balance things out nicely.
By the way, you guys do really nice work. Nice products overall.
I cut my teeth on IBM Series 500's, and was also was once deeply involved in OS/2, with the same result as happened to you. Right now my project is discovering how to permanently disable that annoying Narrator in 8.1 There has to be a Registry key somewhere...
Charley