EzMerge PDF files normally come with a pre-set Unique Identifier that cannot be changed. However, if you are looking to add a prefix to your files, for instance, the name on the product, you can do so by using the "Prefix File Name" menu in the EzMerge field. This menu will contain a list of fields that can be used as the prefix for the file name.
The file will still contain most of the Unique Identifier as it's needed to avoid conflicts, but for those looking to add their own variable, you can do so using this method.
Shown below is an EzMerge template while adds the "Name" as the prefix, this name that's typed into the form can be seen on the file that is downloaded. The format will be: PREFIX-CartID-ItemID-FieldName