I need to change the hanging indent in my document but cannot edit an output style.
Unless you're the EndNote Web Administrator for your site, you won't be able to edit and upload output styles. Happily, you don't need to: the hanging indent can be controlled from within your Word document.
Click Format Bibliography button on the EndNote Web toolbar > select the 'Layout' tab. You will see options for First Line indent and Hanging Indent.
This may be needed to adjust the 'Harvard' style to match some Universities standards.