For this first we will be creating a Managed Property. I have already created a site column which I will be using as Crawled Property while creating the the Managed Property. To create Managed Property go to Central Administration and then go to the FAST Query SSA in the Manage Service Application. Inside the FAST Query SSA find the FAST Search Administration:
Now inside this click on the Managed Property Link:
Set-FASTSearchMetadataManagedProperty –Name LivingLocation -RefinementEnabled $true
Now we need to add the LivingLocation as the refiner property. To do this we need to edit the XML in Filter Category Definition in the Refiner Web Part.
<Category Title="Living Location" Description="Location" Type="Microsoft.Office.Server.Search.WebControls.ManagedPropertyFilterGenerator" MetadataThreshold="1" NumberOfFiltersToDisplay="4" MaxNumberOfFilters="20" ShowMoreLink="True" MappedProperty="LivingLocation" MoreLinkText="show more" LessLinkText="show fewer" ShowCounts="Count" />If the field type is managed metadata field we need to have the type as Microsoft.Office.Server.Search.WebControls.TaxonomyFilterGenerator
Once we add this XMLstring we need to make sure to change few more things in the Web Part. We need to uncheck the Use Default Configuration else the web part will not take the modified XML string.