Redirect original paths to custom ones

There should be an option to redirect original system paths to custom ones, or to free them for use elsewhere.

For example, the following situation in my case has arisen: when customising the user link on a production site, users may still try to login using a bookmark to example.com/user, where they would subsequently reach a 404 page.

Creating an alias from user to [custom] using the Pathauto module doesn't work.
Creating a URL redirect using the Redirect module also doesn't work.

But I found a workaround in that I could create a URL redirect from user to [custom]/login, with a system warning asking me to confirm the action:
"I understand the following warnings and would like to proceed with saving this URL redirect:
The source path user is likely a valid path. It is preferred to create URL aliases for existing paths rather than redirects."