Prevent Office 2013 from creating "Custom Office Templates" directory in My Documents

According to the answer to the question Custom Template location in Office 2013 on the Microsoft Community forums:

You can choose to override this setting by specifying a Personal Templates Folder. This can be done by going to File > Options > Save and manually entering a folder path. This needs to be done for each application, and for any application that does not have a Personal Templates path manually set, Office will create the Custom Office Templates folder the first time you save a template, and will set the Personal Templates path to this location.

Hide the folder under properties. You won't be able to see it but MS Office and Windows can still access it.

• Right-click on the directory
• Select "Properties"
• Check the "Hidden" checkbox under "Attributes"