I am unsure why you would want to do this.
If it is for end user signup - build a custom login/signup page for them using the API and your own frontend, you can omit anything from this you choose, such as “forgot your password”
If you wanted to edit Strapi’s admin login page you can do this by editing the npm package itself and using patch-package to ensure the change is patched and the change is included in source control.