You can change the New document profile. Those are Illustrator files. There has just been a thread about the process yesterday.
If you're referring to this post: https://community.adobe.com/t5/illustrator/is-there-a-way-to-name-and-save-your-custom-document-pres...
There's no information there regarding how to display inches instead of units.
Do you know how to show Rulers for your new document. If you have them showing, try double clicking on the box where the rulers meet (upper left). This should reveal a dropdown menu with a list of measurement options. Click on inches and then name and save the document. Move the newly saved document to the New Document Profile folder in your user account.