Modifying values in Orion.CustomPropertyValues?

No, this is not currently supported. I opened a feature request for it: #402385.

Thanks!

Did this get implemented? I'm looking to add values into this via API.

Direct "Delete" support for Orion.CustomPropertyValues has not been implemented, but you can achieve the same effect by calling ModifyCustomProperty. Like this:

Invoke-SwisVerb $swis Orion.NodesCustomProperties ModifyCustomProperty @(
    "TestProp",               # Name
    "my description here",    # Description
    4000,                     # Size
    @("a", "b")               # Values
)

You must provide the complete list of values you want the property to have. If you provide a subset of the values it currently has, then the list will be trimmed accordingly.