Today I’m visiting a customer who accidentally renamed the Title column in the list item content type. After they discovered that they made a mistake, they tried to rename the column back to “Title”, but SharePoint does not allow this, because you would rename the column to a reserved name.
“The Column name that you entered is already in use or reserved”
The only way to rename this column back to Title, is to talk against the SharePoint object model by writing some custom code. This blog post from Godwin Tenzing provides detailed information about the problem and also shows a quick coding example which allowed me to fix the problem within 5 minutes.