If you mean that you want to type alt-1-3-0 to get é that should always work in Windows, but don't use it for use in a browser. In html you use the 'entity' é That's because the web is more than Windows (it's Mac and Linux and Chinese and Arabic also).

For more exotic characters your preferably use Unicode. That's easy to use in MS Word and easy to use in html, but the ways to do it are different between Windows and the web.
If you're sure it's strictly for use in Windows, you can use characters from, say, Wingdings and Symbol also.

All alt-codes and all unicode-codes are pre-defined. You can't change them and you can't add them. You can only use them.

Kees