How to set date format when manually inserting date on excel, without changing regional settings?

I know exactly what you are talking about. I like to type YY-MM-DD. The setting to change it to what you want is not in Excel. The setting you want is in windows. It is hidden somewhere in the control panel "time and language".

I had to go to an advanced setting "Change Time and Date Format" and change the "Short Date" setting.

Depending on which operating system you use the directions could be a little different.

Hope this helps.