Unassign elements from entitlements?

I see several actions and workflows that will assign Services/Resources/CatalogItems to an Entitlement. However, I do not see any facility to unassign any.

I wondered if I could at least clear one out by setting the vCACCAFEEntitledService[] to an empty array and then updating the entitlement. So I tried:

vCACCAFEEntitlementObj.entitledServices = [];

But this errors with:

[E] Property or method 'entitledServices' not found on object vCACCAFEEntitlement

What's odd though is that in the previous line, I was debugging and did:

System.log("Existing Entitlement Services: " + vCACCAFEEntitlementObj.entitledServices.toSource());

And this works just fine, resulting in a JSobject string that shows the content of the Entitlement services. So entitledServices does seem to exist, but then throws the error on the next line when trying to set it.  ... Very confusing.

Any help would be appreciated.