Set "Add managed property to custom result set" with PowerShell

Hi,

How can I set "<label for="ctl00_PlaceHolderMain_retrivableCheckBox">Add managed property to custom results set retrieved on each query. Note: Only the first 2 kilobytes of data is available for display by default.</label>" with PowerShell for managed property? I mean that setting which you can set in Central Administration for Managed Property. I can create crawled and managed properties and map them, but I need that setting that I can use managed properties in KeywordQueries. Is it a property of ManagedProperty class? In MSDN there was no descriptions for all ManagedProperty class properties, so that was not helpful.

I think I have try everything, but Central Administration UI is not updating and queries are not working.