The SpecializationValues.xml file is located in each web site directory. For example: <SiteName>\SPFServer\SPFConfigService\SPFSharedSettings..
You must ensure that any new interface definition has a higher value than the interface definition that you are implying. You can do this by placing the new interface definition at the bottom of the file and giving the new interface definition a unique number higher than the previous line. For example,
<SpecializationValue value="4070" interface="ISPFIncrementalTemplate"/>
<SpecializationValue value="4071" interface="ISPFVendorDocVersion"/>
<SpecializationValue value="4090" interface="IVTLExportTask"/>
<SpecializationValue value="4093" interface="IVTLImplicitDeleteTask"/>
<SpecializationValue value="4094" interface="IVTLFileExportTask"/>
For more information on creating a unique SpecializationValues.xml file for each custom server project, see Custom settings files for custom server projects.