You can start Word with a different template via the /t command-line switch. See:
https://support.microsoft.com/kb/210565?wa=wsignin1.0
You can simply create a new Word shortcut using that switch. That way, you can choose between starting Word normally, or with your template. There is no need to overwrite the Normal template, though you could do so if you only ever want to use your custom
template.
Cheers
Paul Edstein
[MS MVP - Word]