You can edit an existing document subclass, such as adding new properties to the class, after it is put into production. However, it is not recommended to alter the class. For example, if you created and made available a document class that users assigned to potentially thousands of documents, those documents will need to be re-examined after you change that class.
An added property means adding a column to the database table that contains the document class description. The documents already assigned to that class remain as rows in that table, but there is no value in the new column. The Content Platform Engine property sheets display the new property for the old versions of the document. Thereafter, you can use Content Platform Engine search and bulk operations to find and populate those empty columns. Documents that are checked in under that class after the new property is added have values for the new column in the database table, provided a value was assigned either by the system or by the user.