Are there any questions that people know of about adding your own supplications within amida during the middle 13 brachot, ie. אתה חנן... לאנוש בינה, עזור לי נא להצליח במבחן שלי למחר, וחננו... ?

I'm mostly curious about any opinions which day that you cannot do this. I only found out about this after highschool and I remember one of my classmates complaining to put rabbi about שע because it was the same thing every time. This would have been an easy answer to give to him, but it was not given.

This has tremendously enriched my davening, wish I know about it sooner.