Native Powershell has ways to append values to multi-valued properties in Active Directory. We need to allow that same option in DRA PowerShell. Example use case would be the DynamicGroup WhiteList and BlackList properties. Currently you must enumerate the entire value, remove the desired value and write the entire list back into the object. (Same with values like proxyAddresses, multi-valued DRA Custom Attributes, etc)
We are currently scoping and planning to update the DRA PowerShell behavior and cmdlets in the next few updates in order to simplify using these cmdlets.