After executing SET DATABASE SQL NAMES TRUE the database doesn't allow me to create, for example, a column called DAY.
Since I executed the statement on a database catalog that I had already been working on for a while I would like to know if there's a way to check an existing schema for these violations.
You can make a copy of the database and edit the .script file of the copy to change the existing statement SET DATABASE SQL NAMES FALSE to TRUE. When you open the copy, the engine will stop loading the script and report an error if it encounters a reserved name used for a database object. You can edit the disallowed names and try again until there is no error.