The Excel Services REST and SOAP APIs introduced in SharePoint 2010 are SharePoint only, but with the Excel Services JavaScript API you can work with embedded workbooks on a host web page — from ...

Enabling JavaScript should make Excel more powerful, but increasing access points makes it even more of a web security nightmare than it already is.

You can then edit the data in the Excel file then upload that and it will convert it back to a KML file. Notes: All styles, folders, etc., are lost in the conversion.