Is it possible to add a configuration property to an existing json file? I would like to add a property to

SC.CONFIGURATION.categories

and have it appear next to existing categories options on the Website Configuration page.

Yes. If SCA, you can do it in the source or you can use JSONPath in an extension: • https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_4749956145.html#Modify-JSON-Configuration-Files • https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_4750011023.html#Configuration-Modification-Schema • https://docs.oracle.com/en/cloud/saas/netsuite/ns-online-help/section_4750012866.html#Use-Case-Examples