At present it is not possible to add custom fields to the BoM directly from within EasyEDA. You can of course **Export** a copy of the BoM which will then download a copy of the BoM as a CSV format file. This file can be opened in LibreOffice Calc, Gnumeric or any other spreadsheet program such as Excel and extra columns and data added at that point. If you'd like to see this feature in EasyEDA, submitting it as a **Feature Request** will certainly get it on the ToDo list. :)