Is it possible to update an existing Zimbra ZCS contact using the REST API?

Is it possible to update/modify an existing Zimbra contact (or appointment etc) using the REST API?

I can successfully add a contact but not update a contact - even though the URL I use to add a contact requires a parameter with specific record:

https://myZimbraServer.com/service/home/user@mydomain.com/contacts/MyContactsFolder/?fmt=csv&id=176010

You would think that id=176010 would cause that record to be updated but it doesn't - it adds a new record instead. But without that id I get the error "no such item"! Strange... The documentation is poorly written so that doesn't help either. I know I can use SOAP to do it but I want to avoid the pain of XML! (XML is great, until you have to work with it)

PS. I'm using the Zimbra services from 01.com