1. In your PC make a text file with ñ as it's content. then copy the text file to your storage card.
2. Open the text file with WordPad or any notepad app.
3. use xbar or other apps with a copy and paste function to copy the ñ from the text file.
4. after copying, use your registry editor to go to HKCU\Software\Microsoft\Inbox\PresetMsgs and create (or change) a new string value.
5. sa Value data, use xbar to paste the ñ. press done. That's it.
6. To use the ñ character, go to "insert text" you can see the character there.
Video of how to do this