I have a password that I want to use, but Windows 10 says that I can't because I used it before the reinstall. I want to get around this Windows 10 Home security effort. This is my pc. I bought it. I want to use what I want to use. If someone steals my data that is my business. How do I get around this? Would a complete reformat do it?
This depends on how you are logging on to Windows 10.
Windows 10 presses you hard to log in using a Microsoft Account. On first startup after 10 is installed, it will ask you to add a Microsoft Account and makes it seem like you MUST create one if you do not have one. You can get around this by just refusing and choosing to setup your user-profile without a connected Microsoft Account. If you do this then you should be able to set your password to anything you like.
If, however, you setup your user profile using a Microsoft Account email address then you are bound to the user agreement which requires certain security behaviours of you, such as not reusing an old password. As such, there is no way to change your password back to an older one.
Try creating a new LOCAL administrator account using your preferred password and refuse to link to a Microsoft Account. You can then transfer your user files and delete your old account if you want.