Specify type of custom metadata when adding via AppleScript?

I’ve read through the scripting dictionary entries for DT related to custom metadata (add custom meta data and get custom meta data commands, and the custom meta data property on Record) but cannot determine how to specify the type of a new metadata property that I might add.

How, for example, do I specify that a new custom metadata property is to be of type Set or Date, etc.?

That’s not (yet) possible, usually it’s recommended to set up the preferences first. DEVONthink automatically chooses the type depending on the provided data, e.g. date or number or text. But it’s also possible to change the type afterwards in the preferences.