Hi Jonathan,
Actually, EntityType has the following values: Customer, Customer Lead, Vendor, Employee & Other Name. With the exception of Customer Lead, this field is used by both QuickBooks and Method to distinguish between entity types, Customer Lead being Method only. It is used to organize and control what is available to each. I don’t believe it is possible to enter custom values into this field and even if it is, I advise against it.
Why not use a custom field to control this instead? Would a Yes/No field “IsTrial” not serve the same purpose?
-Audisho