Yes, there will be a workaround it this article, but first... WTF! I mean. Seriously. I have a Microsoft account and when installing Windows 10 it kind of wants me to go that route instead of picking SKIP for now and go with the traditional local user account (which BTW is the secret sauce to the solution).
So I (naturally) used my Microsoft account and soon realized that the user data folder for my account is created with... nothing I like. It's not even using the full part of either my given- or family name. And sure not my full username of my Microsoft account but:
C:\Users\danie\...
I might have OCD but it's painful to see this in e.g. the title of Git Bash. So lets fix it.
There are some solutions stating something like: create another local admin account, rename folder, update registry...; and that's where I stop. I remember the days where you had to reinstall a Windows OS just because you didn't trust the condition of the registry after a while. So, lets pick another route.
Solution
When installing Windows 10:
First, use a normal local account with the username you want.
Second, when done installing, go into your account (Settings > Account) and associate it with a Microsoft account.
Victory!
//Daniel